一个事务中所有对DB的操作是一个不可分割的操作序列，这个性质称为事务的______。
A．孤立性
B．独立性
C．原子性
D．隔离性
参考答案：C
有计划地进行预防接种简称_____________，是预防传染病简便易行的手段。
---Have you ever been here before?
---No. this is the first time that I to the Great Wall.
A comes B have been C came D had been
