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  3. Trees should only be pruned when there is a good and clear reason for doing so and, fortunately, the number of such reasons is s

Trees should only be pruned when there is a good and clear reason for doing so and, fortunately, the number of such reasons is s

admin2020-03-30  34
问题    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.
Why is a special substance painted on the tree?
选项 A、To make a wound smooth.
B、To prevent disease entering a wound.
C、To cover a rough surface.
D、To help a wound to dry.
答案B
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。
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