题目

Trees are useful to man in three important ways: they give him wood and other useful things, they give him cool places, and they help to stop drought and flood. Unluckily, in many parts of the world, man has not found that the third of these points is the most important. Man wants to make money from trees, so he has cut them down in large numbers, only to find that without them he has lost the best friends he had. And also, he is usually too careless to plant and look after new trees. So the forests slowly disappear. This does not only mean that man will have fewer trees. The results ar下列四幅图是我们在实验室或课堂上做过的一些实验．（1）用来探究影响动能大小因素的是______图；（2）用来探究感应电流产生的条件的是______图；（3）用来演示通电导体产生磁场的是______图；（4）能够说明重力势能和动能相互转化成的是______图．