Translate the following sentence into English.
使她感到伤心的是她们的友谊未能经得起时间的考验。
【正确答案】：
WHAT MADE HER SAD WAS THAT THEIR FRIENDSHIP DID NOT STAND THE TEST OF TIME.
【题目解析】：
本题考查主语从句的使用。
句子的主干为"...是..."，同时主语是"使她感到伤心的"——what made her sad做主语变成主语从句，而表语是“她们的友谊未能经得起时间的考验”——their friendship did not stand the test of time，整句即为What made her sad was that their friendship did not stand the test of time.