LD200型SF6检漏仪的微处理器监测传感头的灵敏度达到4000次／秒
参考答案：对
为了选择多个控件，可以按住______键，然后单击每个控件。
____ the chat room ten minutes ago, you would have known what we were talking about! [ ]
A. Had you joined in
B. If you joined
C. If you had joined in
D. Had you joined
