Travel by air has become safe，comfortable，rapid and above all __

Travel by air has become safe，comfortable，rapid and above all ______.
A、cheer
B、interesting
C、cheap
D、easy
【正确答案】：C
【题目解析】：选项C，“cheap”意思是“便宜的”，与“安全、舒适、迅速”一起，构成了乘飞机旅行的多个优点，且符合题干中“above all”所强调的乘飞机旅行的最主要优点，即经济性，所以C选项正确。