Allthestudentsweresweepingthefloor _____
问题:
All the students were sweeping the floor ______ they heard a man ______ "help". [ ]
A. when; shouting
B. while; to shout
C. when; to shout
D. while; shouting
All the students were sweeping the floor ______ they heard a man ______ "help". [ ]
A. when; shouting
B. while; to shout
C. when; to shout
D. while; shouting