I ___________ on the computer when Frank called me last night.
A．work B．will work C．was working D．am working
I ___________ on the computer when Frank called me last night.
A．work B．will work C．was working D．am working
C
【详解】
句意：弗兰克昨晚打电话给我时，我正在用电脑工作。
考查过去进行时。work工作,动词原形；will work一般将来时；was working过去进行时；am working现在进行时。根据题干中“when Frank called me last night”可知此处表示当某件事情发生的时候，另一件事情正在进行，when引导的从句用一般过去时，主句用过去进行时。故选C。