普通晶闸管是一种（）半导体元件。
A、PNP三层
B、NPN三层
C、PNPN四层
D、NPNP四层
参考答案：C
It is not rare in ____ that people in ____fifties are going to university for further education.
A．90s, the
B．the 90s, /
C．90s, their
D．the 90s, their
下列行为中，属于代理行为的是( )。
A．居间行为
B．行纪行为
C．代保管物品行为
D．保险公司业务员的揽保行为
