光敏二极管在测光电路中应处于（）偏置状态，而光电池通常处于（）偏置状态。
A.正向
B.反向
C.零
参考答案：B, C
---How does your brother like the song Two Butterflies?
---Great! He _____ such a beautiful song before.
A．doesn’t hear
B．never hear
C．is never heard
D．has never heard
无线上网卡入网默认资费是什么？（）
A.标准资费
B.最低档套餐
C.中档套餐
D.封顶套餐
