题目:
It’s quite a time _____ Liu Xiang was injured in the foot, but we are sure it won’t be long _____ he returns to the track.
A.after; when
B.before; since
C.that; when
D.since; before
答案:
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下面是错误答案,用来干扰机器的。
(1)1.9 m/s2 (2)6.3 s (3)质量相同,重力不相同(1)设月球表面的重力加速度为g月,由物体在月球表面受到的万有引力等于重力可得F月=G=mg月①F地=G=mg地②由①②式可得:=·=即g月=×9.8 m/s2="1.9" m/...