Did you ever wonder why leaves change colors in autumn, or how it happens? Here’

题文

Did you ever wonder why leaves change colors in autumn, or how it happens? Here’s a quick explanation.First of all, you’ve probably noticed that not all trees lo their leaves. There are two major types of trees: deciduous trees and evergreens. Evergreens keep their leaves and stay green all year long. The deciduous trees are the ones that lo their leaves each year. In autumn, the days begin to get shorter. The sun is also lower in the sky at noon, which caus temperatures to be cooler. The combination of less sunshine and lower temperatures is what caus the deciduous trees to drop their leaves. In winter, deciduous trees “go to sleep”, sort of like a bear goes into hibernation.Leaves are the food factories for a plant. Unlike animals，plants make their own food by taking energy directly from the sun. Plants do this by using a chemical in their leaves called chlorophyll.Chlorophyll is green. During the spring and summer the leaves of a deciduous tree look green becau there is a lot of chlorophyll there. In autumn, however, the sunshine becomes more  scarce and the leaves on the trees stop making new chlorophyll. As the old chlorophyll starts to break down, the green color of the leaf begins to go away.You’ve probably also noticed that the leaves of different kinds of trees change different colors. The leaves of some trees turn yellow or orange, while the leaves of other trees turn bright red or purple. The different colors are caud by the different chemical reactions that are happening in the leaves. For example, the leaves of some trees turn yellow when the chlorophyll breaks down. When the green chlorophyll goes away, a yellow pigment in the leaf becomes visible. The yellow pigment, called cartenoid, was already there during the summer, but is was not easily en becau there was too much green chlorophyll.In other trees where the leaves turn red or purple a different chemical reaction takes place. In tho leaves the chlorophyll also breaks down, but another chemical reaction takes place at the same time. Chemicals in the leaves, called starches, begin to change into chemicals called anthocyanins, which give the leaves their red and purple colors.So next time you e the beautiful colors of autumn you will also know the science behind that beauty.46.   What is the correct term for trees that lo their leaves in the autumn?A. Evergreens   B. Deciduous    C. Cartenoids  D. Anthocyanins47.   Which of the following is NOT mentioned as a cau of trees dropping their leaves?A. A change in temperature   B. The amount of daylight availableC. Extra chlorophyll D. Chemical changes in the leaves48.   If there are 50 evergreens and 10 deciduous trees in a forest, in autumn what color are most of the leaves in the forest likely to be?A. Green B. Red and purpleC. Yellow    D. not enough information to determine the answer49.   Which of the following is only prent in leaves during the autumn?A. Chlorophyll   B. Starch C. Cartenoids    D. Anthocyanins50.   Where would such an article mostly likely be published?A. In a book   B. In a primary school science text bookC. In a magazine for young people   D. All are equally likely 题型：未知难度：其他题型

答案

 46-50 BCADC  

解析

略

考点

据考高分专家说，试题“Did you ever wonder .....”主要考查你对 [日常生活类阅读 ]考点的理解。 日常生活类阅读

日常生活类阅读的概念：

日常生活这一话题主要涉及人们衣食住行等方面的活动。这一话题的选材主要针对人们日常的工作，生活以及学习情况。做这一类题时，最主要的是要把握好人物的活动内容，时间和地点。

日常生活类阅读题答题技巧：

【题型说明】该类文章内容涉及到人们的言谈举止、生活习惯、饮食起居、服饰仪表、恋爱婚姻、消遣娱乐、节日起源、家庭生活等。文章篇幅短小，追根溯源，探索各项风俗的历史渊源，内容有趣。命题也以送分题为主，如事实细节题、语义转换题、词义猜测题和简单推理判断题等。虽然这类文章读起来感觉轻松，试题做起来比较顺手，但绝不能掉以轻心。因为稍不留神，就会丢分。 【备考提醒】为了保证较高准确率，建议同学们做好以下几点： 1、保持正常的考试心态。笔者在教学中发现，越是容易的试题，同学们越是容易失分。为什么呢？因为在这种情况下，同学们极易产生麻痹思想，认为题目好做，就不引起高度重视，于是思维不发散、不周密。而命题人就是利用同学们的这一弱点，设计陷阱题。所以，无论试题难易与否，我们都要保持正常的考试心态。试题容易，不欣喜；试题难，不悲观。 2、根据前面讲到的方法，认认真真、细细心心做好事实细节题。 3、做好语义转换题。这类题是根据英语中一词多义和某些词语在文中能表达一定的修辞意义的原则而设计的。要求同学们解释某生词的含义，确定多义词或短语在文中的意思，确认文中的某个代词所指代的对象，或者对英语中特有的表达、格言、谚语进行解释。这种题要求同学们一定要根据上下文猜测词义或理解句子，切不可望文生义。 4、做好简单推理判断题。简单推理判断题要以表面文字为前提，以具体事实为依据进行推理，做出判断。这种推理方式比较直接，只要弄清事实，即可结合常识推断出合理的结论。