The word “burnout” here refers to the state of（）.

Read the passage and answer the questions.

①Taste is such a subjective matter that we don’t usually conduct preference tests for food. The most you can say about anyone’s preference, is that it’s one person’s opinion. But because the two big cola (可口饮料) companies—Coca-Cola and Pepsi Cola are marketed so aggressively, we’ve wondered how big a role taste preference actually plays in brand loyalty. We set up a taste test that challenged people who identified themselves as either Coca-Cola or Pepsi fans: Find your brand in a blind tasting.
②We invited staff volunteers who had a strong liking for either Coca-Cola Classic (传统型) or Pepsi, Diet (低糖的) Coke, or Diet Pepsi. These were people who thought they’d have no trouble telling their brand from the other brand.
③We eventually located 19 regular cola drinkers and 27 diet cola drinkers. Then we fed them four unidentified samples of cola one at a time, regular colas for the one group, diet versions for the other. We asked them to tell us whether each sample was Coke or Pepsi; then we analyzed the records statistically to compare the participants’ choices with what mere guess-work could have accomplished.
④Getting all four samples right was a tough test, but not too tough, we thought, for people who believed they could recognize their brand. In the end, only 7 out of 19 regular cola drinkers correctly identified their brand of choice in all four trials. The diet-cola drinkers did a little worse-only 7 to 27 identified all four samples correctly.

⑤While both groups did better than chance would predict, nearly half the participants in each group made the wrong choice two or more times. Two people got all four samples wrong. Overall, half the participants did about as well on the last round of tasting as on the first, so fatigue, or taste burnout was not a factor. Our preference test results suggest that only a few Pepsi participants and Coke fans may really be able to tell their favorite brand by taste and price.①Taste is such a subjective matter that we don’t usually conduct preference tests for food. The most you can say about anyone’s preference, is that it’s one person’s opinion. But because the two big cola (可口饮料) companies—Coca-Cola and Pepsi Cola are marketed so aggressively, we’ve wondered how big a role taste preference actually plays in brand loyalty. We set up a taste test that challenged people who identified themselves as either Coca-Cola or Pepsi fans: Find your brand in a blind tasting. 

②We invited staff volunteers who had a strong liking for either Coca-Cola Classic (传统型) or Pepsi, Diet (低糖的) Coke, or Diet Pepsi. These were people who thought they’d have no trouble telling their brand from the other brand.
③We eventually located 19 regular cola drinkers and 27 diet cola drinkers. Then we fed them four unidentified samples of cola one at a time, regular colas for the one group, diet versions for the other. We asked them to tell us whether each sample was Coke or Pepsi; then we analyzed the records statistically to compare the participants’ choices with what mere guess-work could have accomplished.
④Getting all four samples right was a tough test, but not too tough, we thought, for people who believed they could recognize their brand. In the end, only 7 out of 19 regular cola drinkers correctly identified their brand of choice in all four trials. The diet-cola drinkers did a little worse-only 7 to 27 identified all four samples correctly.

⑤While both groups did better than chance would predict, nearly half the participants in each group made the wrong choice two or more times. Two people got all four samples wrong. Overall, half the participants did about as well on the last round of tasting as on the first, so fatigue, or taste burnout was not a factor. Our preference test results suggest that only a few Pepsi participants and Coke fans may really be able to tell their favorite brand by taste and price.①Taste is such a subjective matter that we don’t usually conduct preference tests for food. The most you can say about anyone’s preference, is that it’s one person’s opinion. But because the two big cola (可口饮料) companies—Coca-Cola and Pepsi Cola are marketed so aggressively, we’ve wondered how big a role taste preference actually plays in brand loyalty. We set up a taste test that challenged people who identified themselves as either Coca-Cola or Pepsi fans: Find your brand in a blind tasting. 

②We invited staff volunteers who had a strong liking for either Coca-Cola Classic (传统型) or Pepsi, Diet (低糖的) Coke, or Diet Pepsi. These were people who thought they’d have no trouble telling their brand from the other brand.
③We eventually located 19 regular cola drinkers and 27 diet cola drinkers. Then we fed them four unidentified samples of cola one at a time, regular colas for the one group, diet versions for the other. We asked them to tell us whether each sample was Coke or Pepsi; then we analyzed the records statistically to compare the participants’ choices with what mere guess-work could have accomplished.
④Getting all four samples right was a tough test, but not too tough, we thought, for people who believed they could recognize their brand. In the end, only 7 out of 19 regular cola drinkers correctly identified their brand of choice in all four trials. The diet-cola drinkers did a little worse-only 7 to 27 identified all four samples correctly.

⑤While both groups did better than chance would predict, nearly half the participants in each group made the wrong choice two or more times. Two people got all four samples wrong. Overall, half the participants did about as well on the last round of tasting as on the first, so fatigue, or taste burnout was not a factor. Our preference test results suggest that only a few Pepsi participants and Coke fans may really be able to tell their favorite brand by taste and price.①Taste is such a subjective matter that we don’t usually conduct preference tests for food. The most you can say about anyone’s preference, is that it’s one person’s opinion. But because the two big cola (可口饮料) companies—Coca-Cola and Pepsi Cola are marketed so aggressively, we’ve wondered how big a role taste preference actually plays in brand loyalty. We set up a taste test that challenged people who identified themselves as either Coca-Cola or Pepsi fans: Find your brand in a blind tasting.
②We invited staff volunteers who had a strong liking for either Coca-Cola Classic (传统型) or Pepsi, Diet (低糖的) Coke, or Diet Pepsi. These were people who thought they’d have no trouble telling their brand from the other brand.
③We eventually located 19 regular cola drinkers and 27 diet cola drinkers. Then we fed them four unidentified samples of cola one at a time, regular colas for the one group, diet versions for the other. We asked them to tell us whether each sample was Coke or Pepsi; then we analyzed the records statistically to compare the participants’ choices with what mere guess-work could have accomplished.
④Getting all four samples right was a tough test, but not too tough, we thought, for people who believed they could recognize their brand. In the end, only 7 out of 19 regular cola drinkers correctly identified their brand of choice in all four trials. The diet-cola drinkers did a little worse-only 7 to 27 identified all four samples correctly.

⑤While both groups did better than chance would predict, nearly half the participants in each group made the wrong choice two or more times. Two people got all four samples wrong. Overall, half the participants did about as well on the last round of tasting as on the first, so fatigue, or taste burnout was not a factor. Our preference test results suggest that only a few Pepsi participants and Coke fans may really be able to tell their favorite brand by taste and price.①Taste is such a subjective matter that we don’t usually conduct preference tests for food. The most you can say about anyone’s preference, is that it’s one person’s opinion. But because the two big cola (可口饮料) companies—Coca-Cola and Pepsi Cola are marketed so aggressively, we’ve wondered how big a role taste preference actually plays in brand loyalty. We set up a taste test that challenged people who identified themselves as either Coca-Cola or Pepsi fans: Find your brand in a blind tasting.
②We invited staff volunteers who had a strong liking for either Coca-Cola Classic (传统型) or Pepsi, Diet (低糖的) Coke, or Diet Pepsi. These were people who thought they’d have no trouble telling their brand from the other brand.
③We eventually located 19 regular cola drinkers and 27 diet cola drinkers. Then we fed them four unidentified samples of cola one at a time, regular colas for the one group, diet versions for the other. We asked them to tell us whether each sample was Coke or Pepsi; then we analyzed the records statistically to compare the participants’ choices with what mere guess-work could have accomplished.
④Getting all four samples right was a tough test, but not too tough, we thought, for people who believed they could recognize their brand. In the end, only 7 out of 19 regular cola drinkers correctly identified their brand of choice in all four trials. The diet-cola drinkers did a little worse-only 7 to 27 identified all four samples correctly.
⑤While both groups did better than chance would predict, nearly half the participants in each group made the wrong choice two or more times. Two people got all four samples wrong. Overall, half the participants did about as well on the last round of tasting as on the first, so fatigue, or taste burnout was not a factor. Our preference test results suggest that only a few Pepsi participants and Coke fans may really be able to tell their favorite brand by taste and price.

The word “burnout” here refers to the state of（）.

being seriously burnt in the skin

being unable to bum for lack of fuel

being badly damaged by fire

being unable to function because of excessive use

根据语境“Overall, half the participants did about as well on the last round of tasting as on the first, so fatigue, or taste burnout was not a factor.”总之，有一半的参与者在第一轮和最后一轮表现的差不多，因此(味觉)疲劳，或者说味觉burnout并不是影响因素。