1.“i don’t like to travel. ”“have you ever _____ in an airplane?”a. flying b. flew c. flowed d. flown2.the center of gravity of the human body ______ behind his joint.a. located b. locating c. to locate d. is located3.“today is very cold, isn’t it?” “yes, the river is _____ over.”a. freezed b. freeze c. frozen d. freezing4.“what happened in that new area?” “new houses ______ recently over there.”a. are built b. build c. have built d. have been built5.“when did you go to work?” “as soon as they came, we ______ to work.”a. went b. were going c. had gone d. go6.“did you wait for him very long?” “yes, i ______ to bed until five in the morning.”a. did go b. didn’t go c. had gone d. went7.perhaps it will be a long time ______ from abro