单项选择题
Convection is the principal means （） temperature is equilibrated in liquids and gases.
A.in which B.on which C.by which D.from which
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.
单项选择题 Let H （） the quantity of heat which has been converted into mechanical work.
