问题补充：
------What do you think made Mary so upset?
-------- her new bicycle.
A. As she lost
B. Lost
C. Losing
D. Because of losing
答案：
A. As she lost
B. Lost
(答案→)C. Losing
D. Because of losing
解析：句意：--你认为什么使玛丽那么不安？--丢了她的新自行车。这里第一句中的do you think是插入语，what在句中作主语；第二句是省略句，完整的是Losing her new bicycle made her new bicycle.所以选项必须能够做主语，A是状语从句，B是过去分词，不能做主语； D是原因状语，故选C。
