21. Mary wanted to travel around the world all by herself, but her parents did not _______ her to do so.
A. forbid B. permit C. follow D. ask
22. A fire _______ in the lower story during the midnight and soon the whole building was in flames.
A. was breaking out B. was broken out C. broke out D. break out
23. _______ all these people have in common is ________ they have succeeded.
A. What; that B. That; what C. That; that D. What; what
24. Watch out ______ cars when you cross the road.
A. at B. to C. of D. for