来自：查字典高考网 2014-12-25
Questions 1-13
Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher， the sequoia tree can pump water to its very top， more than 100 meters above the ground. Until the end of the nineteenth century，the movement of water in trees and other tall plants was a mystery. Some botanists hypothesized that the living cells of plants acted as pumps， But many experiments demonstrated that the stems of plants in which all the cells are killed can still move water to appreciable heights. Other explanations for the movement of water in plants have been based on root pressure， a push on the water from the roots at the bottom of the plant. But root pressure is not nearly great enough to push water to the tops of tall trees. Furthermore， the conifers，which are among the tallest trees， have unusually low root pressures.
If water is not pumped to the top of a tall tree， and if it is not pushed to the top of a tall tree， then we may ask， How does it get there？ According to the currently accepted cohesion -tension theory， water is pulled there. The pull on a rising column of water in a plant results from the evaporation of water at the top of the plant. As water is lost from the surface of the leaves， a negative pressure， or tension， is created. The evaporated water is replaced by water moving from inside the plant in unbroken columns that extend from the top of a plant to its roots. The same forces that create surface tension in any sample of water are responsible for the maintenance of these unbroken columns of water. When water is confined in tubes of very small bore， the forces of cohesion （the attraction between water molecules） are so great that the strength of a column of water compares with the strength of a steel wire of the same diameter. This cohesive strength permits columns of water to be pulled to great heights without being broken.
1. How many theories does the author mention？
（A） One
（B） Two
（C） Three
（D） Four
2. The passage answers which of the following questions？
（A） What is the effect of atmospheric pressure on foliage？
（B） When do dead cells harm plant growth？
（C） How does water get to the tops of trees？
（D） Why is root pressure weak？
3. The word demonstrated in line 7 is closest in meaning to
（A） ignored
（B） showed
（C） disguised
（D） distinguished
4. What do the experiments mentioned in lines 7-9 prove？
（A） Plant stems die when deprived of water
（B） Cells in plant stems do not pump water
（C） Plants cannot move water to high altitudes
（D） Plant cells regulate pressure within stems
5.How do botanists know that root pressure is not the only force that moves water in plants？
（A） Some very tall trees have weak root pressure.
（B） Root pressures decrease in winter.
（C） Plants can live after their roots die.
（D） Water in a plants roots is not connected to water in its stem.
6. Which of the following statements does the passage support？
（A） Water is pushed to the tops of trees.
（B） Botanists have proven that living cells act as pumps.
（C） Atmospheric pressure draws water to the tops of tall trees.
（D） Botanists have changed their theories of how water moves in plants.
7. The word it in line 16 refers to
（A） top
（B） tree
（C） water
（D） cohesion-tension theory.
【1995年10月托福阅读全真考题】相关文章：
[标签：海外留学,考试,托福,,]
1000张学生用草稿纸考研专用免邮空白便宜薄演草演算纸白纸本书写纸批发打草a4大张实惠装18k高考数学草稿本
探秘历史 第二季 第211集 此人高考数学考了0分，因作文写3句话被重点大学录取
爆笑班主任 第一季 第220集 高考前最后一只视频，山东王老师揭秘高考的秘密
沈阳音乐学院郎亦农教授的女高音高考曲目解析课程 第1集 沈阳音乐学院郎亦农为你讲解女高音高考曲目
2019全国高考志愿填报攻略 第50集 天津市高考历史三年本科录取排名
创艺第二届：2019届高考录取表彰大会暨“核桃音乐节”合影——你只管努力，剩下的交给创艺
NBA流言收割机 第6集 神预测？高考数学试题暗示猛龙勇士4
张雪峰高考志愿填报指南 第15集 高考填报志愿，想学电子信息类专业，推荐报这六所高校，不出错
衍声高考琴行2019高本硕学生暑假音乐会 张俊瀚《陕北民歌主题变奏曲》《阿根廷舞曲》第三乐章
你高考成绩高吗？这道题目怎能成立？高难度奥数，能不能把你难住
学渣儿子高考，英语选择题全选B！老师通报成绩的那一刻父亲懵了
葛军大爷怒了：高考我出了个小学数学送分题，你们跟我说不会做？
