— How long have you been in this office?

— Just a few minutes．My cousins _______ here together with me．

A．have walked

B．had walked

C．walked

D．have been walking

发现电气设备起火，应迅速切断电源，使用（）扑救。

A.水

B.煤面

C.泡沫灭火器

D.干粉灭火器