每隔（）小时TPOP上将显示夹爪系统油脂加注警报。
参考答案：80
While typing, Helen has a habit of stopping ______ to give her long and flowing hair a smooth.
A now and then B.over and over C.up and down D.here and there
如果一个关系模式R的所有属性都是不可分的基本数据项，则______。
A) R∈1NF B) R∈2NFC) R∈3NF D) R∈4NF
