—Why did you come back so early?

—The English party has been            till next Friday. [ ]

A.put on

B.put off

C.put away

D.put out

（）的形成则主要靠晶体晶体管V12、电容C2、电阻R5、电位器RP组成的积分电路。

A、锯齿波

B、矩形波

C、正弦波

D、方波