问题补充：
Time , we are going to visit the famous military museum before we leave this city.
A. permits
B. to permit
C. permitting
D. being permitted
答案：
A. permits
B. to permit
(答案→)C. permitting
D. being permitted
解析：独立主格结构Time与 permit为主谓关系用现在分词。 时间允许的话在我们离开这座城市前我们去参观军事博物馆。选C
