Tough __________ the task was, we _______ finish it ahead of time and therefore we were highly praised for it.

A．though; would

B．although; had to

C．as; were able to

D．though; must

热传导是由于（）而在同一物体内或者相互接触的物质之间进行热能传递。

A、体积差

B、表面积差

C、温度差

D、重量差