---What made you so sad?--- my wallet.A. LoseB. LosingC. To loseD. Lost

问题补充：

------ What made you so sad?

------ my wallet.

A. Lose

B. Losing

C. To lose

D. Lost

答案：

A. Lose

(答案→)B. Losing

C. To lose

D. Lost

解析：考查非谓语动词。句意：什么让你如此不高兴。——是我丢了我的钱包。结合语境下文为省略句。动名词短语做句子主语，表示抽象动作，故选B。