晶体振荡器即用某些晶体（石英晶体）受力后表面产生电荷的压电效应，测量（）反映压力高低.
A.频率
B.电阻
C.电流
D.电量
参考答案：A
He told us _____ he had done in the past. [ ]
A. all that
B. all which
C. what all
D. that all
标识的两个目的是什么？
