【题目】All the students ______ the floor ________ they heard a man ________“help”.
A. were sweeping;when; shouting B. swept; while; to shout
C. swept; when ; to shout D. was sweeping ;while; shouting
【答案】A
【解析】句意:所有的学生都在扫地,这时他们听到一位男士喊“救命”。be doing when...正在做某事这时发生了某事。故排除BC;短语hear sb doing sth听见某人正在做某事。故选A。