电动仪表主要有电Ⅱ型和电Ⅲ型两种。(设备基本知识)
参考答案：对
Mary _____ yet.I'm waiting for her.[ ]
A. came back
B. has come back
C. hasn't come back
D. was coming back
（）是存储数据库和运行DBMS的物质基础。
A.硬件
B.软件
C.程序
D.内存
