选择答案并给出理由
1. “I don’t like to travel.” “Have you ever___in an airplane?”
A.flying B.flew C.flowed D.flown
2.The center of gravity of the human body___behind his joint.
A.located B.locating C.to locate D.is located
3. “Today is very cold,isn’t it?” “Yes,the river is___over”
A.freezed B.freeze C.frozen D.freezing
4. “What happened in that new area?” “New houses___recently over there.”
A.are built B.build C.have built D.have been built
5. “When did you go to work?” “As soon as they came,we___to work”
A.went B.were going C.had gone D.go