结晶器上下振动一次的时间叫振动周期。
参考答案:对
---Why are you so late?
---I was on the way when it to me that I had left my book home,so I had to fetch it.[ ]
A. occurred
B. hit
C. happened
D. reminded
从心理学角度来讲,人格中的个性心理特征是指需要、动机、兴趣等特质。