阅读理解 Trees should only be pruned when there is a good and clear reason for doing so and, fortunately, the number of such reasons is small. Pruning involves the cutting away of overgrown and unwanted branches, and the inexperienced gardener can be encouraged by the thought that more damage results from doing it unnecessarily than from leaving the tree to grow in its own way.
First, pruning may be done to make sure that trees have a desired shape or size. The object may be to get a tree of the right height, and at the same time to help the growth of small side branches which will thicken its appearance or give it a special shape. Secondly, pruning may be done to make the tree healthier. You may cut diseased or dead wood, or branches that are rubbing against each other and thus cause wounds. The health of a tree may be encouraged by removing branches that are blocking up the centre and so preventing the free movement of air.
One result of pruning is that an open wound is left on the tree and this provides an easy entry for disease, but it is a wound that will heal. Often there is a race between the healing and the disease as to whether the tree will live or die, so that there is a period when the tree is at risk. It should be the aim of every gardener to reduce that risk of death as far as possible. It is essential to make the area, which has been pruned, smooth and clean, for healing will be slowed down by roughness. You should allow the cut surface to dry for a few hours and then paint it with one of the substances available from garden shops produced especially for this purpose. Pruning is usually without interference from the leaves and also it is very unlikely that the cuts you make will bleed. If this does happen, it is, of course, impossible to paint them properly.
单选题 46.Pruning should be done to______.
【正确答案】 B
【答案解析】根据文中第二段的“pruning may be done to make sure that trees have a desired shape or size”可知，修枝是为了确保树木按照所需要的形状或大小生长。据此可知，B项正确。
单选题 47.Trees become unhealthy if the gardener______.
【正确答案】 A
【答案解析】根据文中第二段的“The health of a tree may be encouraged by removing branches that are blocking up the centre”可知，为了促进树木的健康，可以将堵塞中部的树枝剪去。据此可知，树木中部的树枝太多不利于树木的健康，A项正确。
单选题 48.Why is a special substance painted on the tree?
【正确答案】 B
【答案解析】根据文中第三段的“One result of pruning is that an open wound is left on the tree and this provides an easy entry for disease…and then paint it with one of the substances available from garden shops produced especially for this purpose”可知，剪枝会在树木的表面留下伤口，从而使树木易于感染病害。据此可知，在树木切口表面漆上特殊的材料就是为了防止病害从树木切口进入，因此B项正确。
单选题 49.A good gardener prunes a tree______.
【正确答案】 C
【答案解析】根据文中第一段的“more damage results from doing it unnecessarily than from learing the tree to grow in its own way．”可知，不必要的剪枝会给树木带来更多的伤害。据此可知，好的园丁只是在必要的时候才修剪树木，C项正确。
单选题 50.What was the author's purpose when writing this passage?
【正确答案】 A
【答案解析】本文首先指出只有在有益于树木的前提下才应修剪树木；后面举例具体说明在何种情况下修剪树木，如确保树木按照所需要的形状或大小生长、促进树木的健康，并且详细介绍了原因和方法。据此可知，作者的目的是在修剪树木方面给予实践指导，A项正确。