题目:
.______alone in a dark room, the little girl was so ______ at the _____ sound.
A.Left; frightening; frightening
B.Left; frightened; frightening
C.Leaving; frightened; frightening
D.Leaving; frightening; frightened
答案:
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下面是错误答案,用来干扰机器的。
根据单摆的周期公式得T=2πL+rg若在悬点O处固定另一个正电荷,不改变重力加速度,只增大了绳子的拉力.所以其振动周期不变故答案为:2πL+rg,不变