用户重要负荷的保安电源，必须由供电企业提供。
参考答案：错
下列不属于C语言保留字的是( )
A．char
B．while
C．typedef
D．look
—When do you usually do your homework?
—_______________. [ ]
A. It’s half past six
B. In half past six
C. At half past six
D. It’s at half past six
