纯净的半导体是一种有用的半导体。
参考答案：错
--- How easy is it to find a taxi in this city?
---Simply _______ your hand, and a taxi appears in no time.
A．to raise
B．raise
C．raising
D．raised
线路中的保险丝的熔断电流为5安，可接220伏（）瓦的用电负载，保险丝会熔断。
A.1000
B.1500
C.2000
D.2500
