Trees should only be pruned (修剪) when there is a good and clear reason for doing so and , he 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  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 out 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 center 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 (愈合) . 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 important 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 materials available from garden shops produced especially for this purpose . Pruning is usually done in winter , for then you can see the shape of the tree clearly without interference (妨碍) 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 .

 

68.Why should running be done ?

       A.To make the tree grow taller .           B.To improve the shape of the tree .

       C.to get rid of the small ranches .         D.To make the small branches thicker .

69.Trees become unhealthy if the gardener         .

       A.To help a wound to dry .

       B.To cover a rough surface .

       C.damages some of the small side branches

       D.Allows too many branches to grow in the middle

70.Why is a special material painted on the tree ?

       A.To help a wound to dry .          B.to cover a rough surface .

       C.To make a wound smooth .     D.To prevent disease entering a wound .

71.A good gardener prunes a tree         .

       A.several times throughout the year    B.as quickly as possible

       C.occasionally when necessary          D.regularly every winter

72.What was the author’s purpose when writing this passage ?

       A.To discuss different methods of pruning .

       B.To introduce some common knowledge of pruning .

       C.To explain how trees develop disease .

       D.To give practical instruction for pruning a tree .

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