一套开关电源系统至少需要()个开关电源模块并联工作。
A.1个
B.2个
C.3个
D.4个
参考答案:B
There's something wrong ______ Gina and Greg. They haven't talked to each other for over one month. [ ]
A. beside
B. between
C. during
D. under
万能表看读数时目光应当和表面垂直,不要()否则读数将有误差。