Question

—What were you doing this time yesterday?
—I _______ some cleaning at home.

A．am doing

B．was doing

C．do

D．did

Answer 1

B

此题考查现在进行时的基本结构。根据上文，昨天这个时候你在正在做什么？可知下文描述的是过去某时正在进行的动作，故用过去进行时态，选B。