— Why are we always having examinations?

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问题选择题

— _____ whether we have grasped the knowledge in every subject.

[ ]

A. Test

B. Testing

C. To test

D. Tested

答案

答案：C

多选题

如图所示，一简谐横波沿x轴向正方向传播，轴上M、N两点相距21m．t=0时M点在平衡位置且向y轴负方向运动，N点为波谷；t=0.5s时M点为波谷，则该波的（　　）

A．波长可能是16.8m

B．周期可能是0.4s

C．波速可能是6m/s

D．波速可能是5m/s

选择题

Anyone can borrow books from this library _______ he keeps them clean and returns them in time.

A．even if

B．unless

C．so that

D．as long as