可引起肝脏疾病的主要有()
A.钙
B.铜
C.钾
D.钠
E.铁
参考答案：B, E
Since 1994, the glacier in Antarctica has lowered by as much as 90cm, ______________sea level to rise.
A．having caused
B．causing
C．caused
D．being caused
在电原理图中，“PTT”表示（）。
A.控发开关
B.天线开关
C.静噪开关
D.功率开关
