Passage 8
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 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 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 diseases,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,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.
What was the author’s purpose when writing this passage?（ ）
A选项：探讨不同的修剪方式，文章中并没有探讨不同的修剪方式；B选项：介绍了一些修剪常识；C选项：解释树木怎样生病，这只是属于文章的一部分内容；D选项：给出一些修剪树木的实际操作，文章中并没有介绍如何操作。浏览文章脉络可知整个文章都为围绕修剪常识展开的，故正确答案是选项B。
下列关于公司的表述，正确的是（）
以下各项列举了我国常见气象灾害与其发生地区的对应关系，其中正确的一项是（）
根据电视收视率调査，看体育节目的观众中青年人比中老年人要多。
由此可推断出（）
—种海洋蜗牛产生的毒素含有多种蛋白，把其中的一种给老鼠注射后，会使有两星期大或更小的老鼠陷入睡眠状态，而使大一点的老鼠躲藏起来。当老鼠受到突然的严重威胁时，非常小的那些老鼠的反应是呆住，而较大的那些老鼠会逃跑。
以上陈述的事实最有力地支持了以下哪项假说？（）
疾病控制中心对某校髙中三个年级的学生进行抽样做视力状况调查，抽样的方法为分层抽样（按比例抽样），若高中一、二、三年级学生人数分别为626、703、780，样本容量为84，则应从离二年级抽样的学生人数为多少？（）
