语法与词汇
While they were away on vocation, they allowed their mail to (be accumulated) at the post office.
【正确答案】
C
【答案解析】be piled up“堆积”。be decreased“减少”；be delivered“邮递，传递”；be returned“返回到…”。由上可知，be accumulated意思最接近的词组为be piled up。本题译文：在外度假时，他们就让自己的信件堆积在邮局。