从第三代计算机开始，（）成为制造计算机核心元件的主要材料
A.硅
B.真空管
C.晶体管
D.铜
参考答案：A
It's very hot in this room. Why don't you _____ your coat? [ ]
A. put on
B. put away
C. take off
D. get off
专家鉴定组成员在哪些情形下应当回避？
