单项选择题
（） the bodies are, （） the friction will be.
A.The smoother；the greater B.Smoother；less C.The rougher；the greater D.rougher；greater
单项选择题 Convection is the principal means （） temperature is equilibrated in liquids and gases.
单项选择题 If you （） the equipment more carefully before sail, we （） so much trouble now.
单项选择题 We’ve tried many ways, but all in vainOnly in this way, （） the problem, I’m sure.
