关闭图标
log图标

toefl.viplgw.cn

  • 使用手机注册
  • 使用邮箱注册
  • 手机号不能为空!

    验证码不能为空!

    用户名不能为空!

    密码不能为空!

  • 邮箱不能为空!

    验证码不能为空!

    用户名不能为空!

    密码不能为空!

已有账号? 登录到雷哥托福
关闭图标
log图标
  • 使用手机找回密码
  • 使用邮箱找回密码
  • 手机号不能为空!

    验证码不能为空!

    密码不能为空!

  • 邮箱不能为空!

    验证码不能为空!

    密码不能为空!

又想起来了
加入生词本

listen

英['lɪs(ə)n] 美['lɪsn]
vi. 听,倾听;听从,听信
n. 听,倾听

已添加
×

我要举报草莓小菇凉评论

用户头像
草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

请选择举报类型:

举报电话:400 1816 180    举报QQ:2095453331
×
logo图标
分享到雷哥托福

分享成功图标分享成功

邀请名师点评成功,管理员正在安排老师进行点评。

继续做题 返回首页
支付雷豆失败图标 雷豆余额不足 购买雷豆 返回
报告题目错误
请选择错误类型:
请描述一下这个错误:

取消

题库 > 阅读-11399-TPO-01

The transition from forest to treeless tundra on a mountain slope is often a dramatic one. Within a vertical distance of just a few tens of meters, trees disappear as a life-form and are replaced by low shrubs, herbs, and grasses. This rapid zone of transition is called the upper timberline or tree line. In many semiarid areas there is also a lower timberline where the forest passes into steppe or desert at its lower edge, usually because of a lack of moisture.

The upper timberline, like the snow line, is highest in the tropics and lowest in the Polar Regions. It ranges from sea level in the Polar Regions to 4,500 meters in the dry subtropics and 3,500-4,500 meters in the moist tropics. Timberline trees are normally evergreens, suggesting that these have some advantage over deciduous trees (those that lose their leaves) in the extreme environments of the upper timberline. There are some areas, however, where broadleaf deciduous trees form the timberline. Species of birch, for example, may occur at the timberline in parts of the Himalayas.

At the upper timberline the trees begin to become twisted and deformed. This is particularly true for trees in the middle and upper latitudes, which tend to attain greater heights on ridges, whereas in the tropics the trees reach their greater heights in the valleys. This is because middle- and upper- latitude timberlines are strongly influenced by the duration and depth of the snow cover. As the snow is deeper and lasts longer in the valleys, trees tend to attain greater heights on the ridges, even though they are more exposed to high-velocity winds and poor, thin soils there. In the tropics, the valleys appear to be more favorable because they are less prone to dry out, they have less frost, and they have deeper soils.

There is still no universally agreed-on explanation for why there should be such a dramatic cessation of tree growth at the upper timberline. Various environmental factors may play a role. Too much snow, for example, can smother trees, and avalanches and snow creep can damage or destroy them. Late-lying snow reduces the effective growing season to the point where seedlings cannot establish themselves. Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes. Some scientists have proposed that the presence of increasing levels of ultraviolet light with elevation may play a role, while browsing and grazing animals like the ibex may be another contributing factor. Probably the most important environmental factor is temperature, for if the growing season is too short and temperatures are too low, tree shoots and buds cannot mature sufficiently to survive the winter months.

Above the tree line there is a zone that is generally called alpine tundra. Immediately adjacent to the timberline, the tundra consists of a fairly complete cover of low-lying shrubs, herbs, and grasses, while higher up the number and diversity of species decrease until there is much bare ground with occasional mosses and lichens and some prostrate cushion plants. Some plants can even survive in favorable microhabitats above the snow line. The highest plants in the world occur at around 6,100 meters on Makalu in the Himalayas. At this great height, rocks, warmed by the sun, melt small snowdrifts.

The most striking characteristic of the plants of the alpine zone is their low growth form. This enables them to avoid the worst rigors of high winds and permits them to make use of the higher temperatures immediately adjacent to the ground surface. In an area where low temperatures are limiting to life, the importance of the additional heat near the surface is crucial. The low growth form can also permit the plants to take advantage of the insulation provided by a winter snow cover. In the equatorial mountains the low growth form is less prevalent.

According to paragraph 3, which of the following is true of trees in the middle and upper latitudes?

  • At the upper timberline the trees begin to become twisted and deformed. A Tree growth is negatively affected by the snow cover in valleys B Tree growth is greater in valleys than on ridges. C Tree growth on ridges is not affected by high-velocity winds. D Tree growth lasts longer in those latitudes than it does in the tropics.
正确答案: A

网友解析

当前版本由 十三个 更新于2018-10-21 21:08:41 感谢由 十三个 对此题目的解答所做出的贡献。

题目解析:以middle and upper latitudes做关键词定位至原文第三四两句,说中高纬度地区树木在很大程度上受到积雪覆盖的时长和深度的影响,山谷地区积雪深,时间长,所以树长得不好,所以是negatively affected,选项B和C与原文相反,D所做比较原文没有提到。

当前版本由 joannazz 更新于2017-12-05 15:41:46 感谢由 joannazz 对此题目的解答所做出的贡献。

根据the middle and upper latitudes定位到第2-4句,说中高纬度地区树木在很大程度上受到积雪覆盖的时长和深度的影响,山谷地区积雪更深,时间更长,所以山脊的树长得更高,那么山谷的树就是negatively affected,选项BCD与原文相反

我有更好解析

取消

提交

题目讨论 (1条评论)

  • 用户头像

    lmyxpjy

    C:文中有although,说明有wind和贫瘠土壤有负面影响。A:比较隐晦,文中说雪的因素盖过了wind和贫瘠土壤。

    • (1)
    • (0)
    • 回复(0)

    2020-05-17 09:28:38

  • 1

解析提交成功,正在审核中

知道了

您已提交评论成功

确定

答案都没有怎么前进?

知道了

此来源单项已做完

知道了

是否确认删除?

取消

删除