安全电压分几个等级（）。
A.3个
B.5个
C.4个
D.2个
参考答案：B
When the time came to make the final decision for a course , I decided to apply for the one that（）my interest.
A. limited
B. reserved
C. reflected
D. spoiled
正“与”门是负“非”门还是负“或”门？
