下列物质哪种是混合物：（）？
A.水
B.空气
C.食盐
D.生石灰
E.二氧化碳
参考答案：B
—Need I wash your car after repairing it?
—Yes, that would be much _______. [ ]
A. good
B. well
C. better
D. best
目前我国卫星的主结构采用的形式有哪些？
