单项选择题
（）, the motion would continue indefinitely once it had started.
A.Were there loss of energy by friction B.Since there be loss of energy by friction C.Were there no loss of energy by friction D.Should be no loss of energy by friction
单项选择题 （） the bodies are, （） the friction will be.
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.
