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问题: 大学英语2 阶段作业3 系列问题6 需给出详细解

6._________six years since I began studying English.
A.They have been
B.It is
C.It was
D.There are

解答:

A
since 完成时标志。
since 后接时间点或一般过去时(瞬间动作), 但所在主句要是完成时。