—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
网友回答
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。