Question

【题目】When they walked along the river，they suddenly heard somebody ________ for help．
A.called
B.call
C.to call
D.calling

Answer 1

【答案】D
【解析】句意“当他们沿着河走的时候，他们突然听到某人在求救。”此处heard somebody calling表示听到某人正在喊，所以要用进行时态，故填D。