实验室一旦出现火情，应立即切断电源，积极进行灭火，火势无法控制时应马上逃离现场并迅速报警。
参考答案：对
Helen has two sisters and a brother. Her brother is working, but _________her sisters are still at school.
A．neither
B．either
C．all
D．both
当数据库的存储结构改变时，可相应修改______，从而保持模式不变。
