问题详情：
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，但它也许是因为吃得太多了。根据前句“I'm not sure of the reason for the dog's illness”可知，这里为不肯定的推测，故用may/might have done “可能做某事”；由于dog's illness与cause之间为被动关系，故*为may/might have been caused。
知识点：虚拟语气与情态动词
题型：阅读填空
