There is very simple way of measuring the height of a water-tower, which we cannot measure

There is very simple way of measuring the height of a water-tower, which we cannot measure by climbing.
Suppose, for example, that we wish to find out the height of the water-tower, AB, in a factory. We first of all go to where the water-tower is standing and measure a distance of, say, 25 feet from it. Then we take a stick, and stand it in the ground at the spot we have just marked.
Let us suppose the stick we are using is 4 feet in height. We now walk farther away from the water –tower in the same straight line as when we measured off the distance of 25 feet. We go from the water-tower until we come to point E, where with our head on the ground, we see the top of the stick and the top of the water-tower in the same height line---that is, the top of the stick just covers the highest part of the water-tower. Every schoolboy can work out the height of the water-tower now.
Suppose that the line CE is five feet. We know that the stick is 4 feet high and the distance BE is 30 feet. Thus, 5 is to 4 as 30 is to AB.
【小题1】If we want to know how high a tall tree is, .
A. we have to climb up the tree
B. we have no way out
C. we must cut down the tree
D we needn’t climb up the tree
【小题2】 According to the passage, which of the following is correct?

【小题3】It is clear from this that the problem can be settled by .A．a childB．the boy who has little schoolingC．everyoneD．a girl at middle school【小题4】To measure a water-tower in this way, .A．no tool is neededB．Besides a stick, tape-measure (卷尺) or at least a ruler is necessary.C．we have to use nothing but a stick D．we have to prepare a set of expensive toolsD

(答案→)D 解析：文章交给读者一个简便的测量水塔的方法，不需要爬高，只需要一根树棍和一些中学的知识。【小题1】细节题：从第一段的句子：There is very simple way of measuring the height of a water-tower, which we cannot measure by climbing.可知要想测量大树的高度，不必要爬树，选D【小题2】细节题：从二三两段的描述，可知A是正确的。【小题3】细节题：从第三段的句子：Every schoolboy can work out the height of the water-tower now.可知学校的学生可以算出这个问题。选D【小题4】细节题：从第二段的句子：Then we take a stick, and stand it in the ground at the spot we have just marked.可知用这种测量方法只需要一个树棍。选C。

就是这个解释