Don't worry. They'll come to help us ___
问题:
Don't worry. They'll come to help us _______.[ ]
A. in half an hour
B. in a half hour
C. after half an hour
D. after a half hour
Don't worry. They'll come to help us _______.[ ]
A. in half an hour
B. in a half hour
C. after half an hour
D. after a half hour