单项选择题
He is over fifty, but he looks as if he（）only in his thirties.
A.is B.were C.will be D.has been
单项选择题 Is there any reason（）you should go away?
单项选择题 Such changes can alter the social structure,（）people to move.
单项选择题 Cycling is a good exercise.（）, it doesn't pollute the air.
