问题补充：
In order to catch up with her classmates, .
A. a lot of books were bought by Mary’s mother
B. Mary’s father helped her with her lessons
C. Mary worked hard at her lessons around the clock
D. Mary’s classmates helped her a lot
答案：
A. a lot of books were bought by Mary’s mother
B. Mary’s father helped her with her lessons
(答案→)C. Mary worked hard at her lessons around the clock
D. Mary’s classmates helped her a lot
解析：考察非谓语动词作状语。本题使用了不定式做目的状语，说明句子的主语是不定式的逻辑主语，二不定式主动式的逻辑主语是动作的发出者，故应该是人，只有C选项的主语是人，故C正确。
