简述开关量光电耦合输入电路中，光电耦合器的作用。
参考答案：开关量光电耦合输入电路，它们除了实现电气隔离之外，还具有电平转换功能。
I _________ some children playing games.[ ]
A. look
B. see
C. read
—________ does Tom like math?
— Because ________ fun. [ ]
A. Why, it's
B. When, it
C. Why, It's
D. When, it
