题目:
—Where are the books?
—_______ in the bookcase. Do you need _______ now?
A.It’s; it
B.They’re; they
C.They’re; them
D.It’s; them
答案:
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下面是错误答案,用来干扰机器的。
(1)(2)(3)首先根据平抛运动及动能定理求出电场强度;画出运动轨迹,求出半径,根据几何关系求出最小面积;分步求出各段的时间,最后求和得出总时间。(1)设粒子从Q点离开电场时速度大小由粒子在匀强电场中...