A：___Mr.and Mrs.Black___?B:They are playing chess.
问题描述：
A：___Mr.and Mrs.Black___?B:They are playing chess.
答
What are doing
看到答语 A + am/is/are + doing Sth.某人正在做什么的,就可以用它相对应的问句" What + am/is/are + A doing?" 来提问.