It was not until yesterday ______ he ret

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问题选择题

It was not until yesterday ______ he returned _______ to know the news. [ ]

A. that ; that I got

B. when ; that did I get

C. when ; that I got

D. that ; that did I get

答案

答案：C

多项选择题

对于（）无线电业务，仅靠测场强值是不足以分析接收质量的，还需要测量误码率。

A.GSM

B.SSB

C.DCS

D.DAB

多项选择题

如图（a）所示，两平行正对的金属板A、B间加有如图（b）所示的交变电压，一重力可忽略不计的带正电粒子被固定在两板的正中间P处。若在t₀时刻释放该粒子，粒子会时而向A板运动，时而向B板运动，并最终打在B板上。则t₀可能属于的时间段是（）