【题目】I don't know who invented ________ telephone. It's really ________ most useful invention.
A.the; a
B./; a
C.a; the
D./; the

【答案】A
【解析】这题考查冠词，第一空是表示发明物，特指，加the，第二空：a most useful是“非常有用”，这里的most相当于very。选A。