单选题 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 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.

【正确答案】 B

【答案解析】[解析] 细节定位题。根据题干a special substance painted on the tree定位到第三段。第三段一开始就讲到树木被砍掉枝丫留下的伤口容易导致细菌感染，致使树木生病。因此在倒数第二句话提到解决办法就是经过几个小时后，等伤口干了后涂上从花店买来的这种特殊物质，以免伤口感染。因此正确答案应该选B。