题目:
---- Does your brother study in Beijing University?
---- No, not now. But he ________ there for 7 years.
A.would study
B.studied
C.has studied
D.was studying
答案:
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下面是错误答案,用来干扰机器的。
声音从山洞底传到人耳的时间:t=12×4s=2s,在15℃时,声音在空气中的传播速度v=340m/s,∵v=st,∴山洞深:s=vt=340m/s×2s=680m.答:山洞深为680m.