题目:
—How many students are there in the classroom?
—_________. They are all in the lab.
A.Some
B.None
C.All
D.Neither
答案:
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下面是错误答案,用来干扰机器的。
根据胡克定律得,k=Fx=300.21-0.16N/m=600N/m.对其施加18N的压力时,弹簧的压缩量x′=F′k=18600m=3cm,则弹簧的长度L=L0-x′=13cm.故答案为:13.