单项选择题
下面哪一个型号的单片机是国产宏晶单片机？
A、STC89C516
B、AT89S51
C、CC2431
D、DS2250
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- 未知题型 Trees should only be pruned(修剪)when there is a good and clear reason for doing so and，fortunately, the number of such reasons is small.Pruning involves 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 trees to grow in their own ways. 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 out diseased or dead wood, or branches that are rubbing against each other and thus causing wounds.The health of a tree may be encouraged by removing the branches that are locking 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 diseases，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, or that there is a period when the tree is at risk.It should be the aim of every gardener to reduce the risk 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 done in winter, for then you can see the shape of the tree clearly without the interference(妨碍)from the leaves and it is, too, very unlikely that the cuts you make will bleeD.If this does happen, it is, of course, impossible to paint them properly. Why should pruning be done?A.Because it can make trees grow taller.B.Because it can improve the shape of the trees.C.Because it can get rid of the small ranches.D.Because it can make the small branches thicker.Trees become unhealthy if the gardener_________.A.to helps a wound to dryB.to covers a rough surfaceC.damages some of the small side branchesD.allows too many branches to grow in the middleWhy is a special material painted on the tree?A.Because it can help a wound to dry.B.Because it can cover a rough surfacE.C.Because it can make a wound smooth.D.Because it can prevent disease entering a wounD.A good gardener prunes a tree_________.A.several times throughout the yearB.as quickly as possibleC.occasionally when necessaryD.regularly every winterWhat 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.请帮忙给出每个问题的正确答案和分析，谢谢！
