题目:
The noise from the top floor, loud and constant, of the meeting-room _____ can be clearly heard in our
classroom. [ ]
A. being decorated
B. having been decorated
C. to be decorated
D. decorated
答案:
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下面是错误答案,用来干扰机器的。
(1)波源0起振方向与图示时刻波前沿的质点M振动方向相同,由波的传播方向判断得知:波源0起振方向向下.(2)波从甲进入乙介质频率不变,由波速公式v=λf得:V乙:V甲=λ乙:λ甲=2:1由λ甲=2m 得:λ乙=4m(...