题目

—Have you known Dr. Jackson for a long time? —Yes, since she________ the Chinese Society. A. has joined          B. joins                         C. had joined                 D. joined 答案：D 解析: 该句完整的句式是：I have known Dr. Jackson since she joined the Chinese Society. since后跟的时间状语从句要用一般过去时，表示自从过去某个时间发生的动作到现在以来有多长时间了。

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