Most of us know we should cut down on fat, but knowing such things isn’t much help when it ________ shopping and eating.

A．speaks of

B．refers to

C．comes to

D．focuses on

由于系统内部温度差的作用，使流体各部分相互混合从而产生的（）现象称为自然对流传热

A、传热

B、对流

C、传导