小孩子吃火龙果尿红色:drop out/drop off/drop behind

drop out:

退出,退学

例句与用法:
1. The marathon runner raced ahead in the early stages of the race but he had overplayed his hand and had to drop out exhausted with only three miles to go.
这位马拉松赛跑者在比赛的开始阶段跑在前面，但他过高地估计了自己的力量，结果在离终点仅3英里时，跑得筋疲力尽力而不得不退出比赛。

2. He drop out because of the pressure.
由于校规很严，所以他退学了。

drop off:

vt. 减弱(减少,掉落)

例句与用法:
1. Business dropped off sharply during the recession.
在经济衰退期间，生意大大减少了。

2. I drop off and miss the end of the film.
我打了个盹儿，把影片的结尾给错过了。

3. Sales dropped off in the fourth quarter.
销售量在第四个季度减少了

4. Interest in the book began to drop off.
人们对这本书的兴趣开始减退了。

drop behind:

vt. 落伍(落后,落在...之后)

例句与用法:
1. Soon I dropped behind the rest of the class.
不久我就落在班上其他同志后面了。

2. John and Jack had dropped behind in order to be alone and have a talk.
为了能单独在一起谈谈，约翰和杰克故意走在别人后面。

she ____dropped behind ____ in her schoolwork.

她的成绩退步了

drop out (不再与大家一起做正在做的事)
drop off (打磕睡)
drop behind in (落后于某事)
故应选(C)

选C呀。
是“落后, 落伍”的意思。