火灾自动报警系统的主电源应采用消防电源，（）使用电源插座。
A、可以
B、不得
C、应当
D、严禁
参考答案：D
填空。
1. This is a ________ mouse. That's a ________ elephant. (small, big)
2. Tom's is ________. Mary's is ________. (new, old)
3. The rabbit (兔子) has very ________ ears.
The cat has very ________ ears. (long, short)
关系模型中，一个关键字()。
A．可由多个任意属性组成
B．至多由一个属性组成
C．可由一个或多个其值能惟一标识该关系模式或任何元组的属性组成
D．以上都不是
is ________. Mary's 
is ________. (new, old)
The rabbit (兔子) has very ________ ears.
The cat has very ________ ears. (long, short)