流体的粘性产生机理是什么？
参考答案：
液体主要是由于液体分子之间的吸引力产生的，气体主要是因为气体分子做不规则运动的动量交换产生阻力而产生的。
在森林里不允许随地丢弃透明饮料瓶，这是由于雨水进瓶后对光的作用相当于一个 _________ 镜，它对太阳光的 _________ 作用，可能导致森林火灾．
小题1:What about _______(see) our teacher later on?
小题2:It takes me half an hour ______(work)out this question.
小题3:It was raining ______ (heavy) at this time yesterday.
小题4:I hope I’ll be a teacher when I ________(grow) up.
小题5:Who is the _________ (tall) Bill, John or Jim?
小题6:Would you please ________ (show) me your photos?
小题7:Look! Who is ________(draw) on the blackboard?
小题8:I always ________(go) to bed at 10:30.
小题9:What ______ you ______(buy) in the supermarket just now?
