以下哪些是主令电器（）
A.真空接触器
B.控制按钮
C.万能转换开关
D.主令控制器
E.互感器
参考答案：B, C, D
AIDS is said __________ the biggest health challenge to both men and women in that area over the past few years.
A．that it is
B．to be
C．that it has been
D．to have been
