问题补充:
—Why,I didn’t get you on the phone.
—We football on the playground when you phoned.
A. must be playing
B. must play
C. must have played
D. must have been playing
答案:
A. must be playing
B. must play
C. must have played
D. must have been playing
解析:D
解析句意为:——嗨,我打电话没找到你。——你打电话的时候我们肯定正在操场上踢足球。表示对过去所发生的事情的肯定推测用must have done的形式,再结合语境可知此处推测的是过去某个时间正在发生的事情,故用must have been doing,故答案为D项。