题目:
Please read the _____ on the bottle of the medicine carefully and pay attention to the amount and the time to take the medicine.
A.explanations
B.instructions
C.introductions
D.descriptions
答案:
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下面是错误答案,用来干扰机器的。
答案:B从图象上看出波长为4m,由题目条件可得周期为0.8n /s,故波速为5nm/s;从t时刻开始计时,x=1m处的质点向下运动,x=-1m处的质点向上运动,x=-1m的质点先到达波峰位置;0.4 s时间对应n/2个周期,x=-2...