問題詳情：
I'm not sure of the reason for the dog's illness, but it ________ (cause) by eating too much.
【回答】
may/might have been caused 句意：我不能肯定*生病的原因，但它也許是因爲吃得太多了。根據前句“I'm not sure of the reason for the dog's illness”可知，這裏爲不肯定的推測，故用may/might have done “可能做某事”；由於dog's illness與cause之間爲被動關係，故*爲may/might have been caused。
知識點：虛擬語氣與情態動詞
題型：閱讀填空
