单项选择题
（）not for gravity，there would be lots of things we could not do.
A.If it isB.Were itC.If it beingD.It were
单项选择题 She preferred that he（）it in the kitchen.
单项选择题 The originally clean river is now seriously polluted and unfit（）.
单项选择题 Never（）such a nice chair.
