屏蔽就是用屏蔽体把（）与测量装置隔开，使信号不受外界（）的影响。
参考答案：外界干扰；电磁场
I ______ my homework, don't talk with me. [ ]
A. am doing
B. is doing
C. do
D.can do
※ [7～10]. ( 3 )
A．
B．
C．
D．
