小站备考
托福
托福听力
Official37听力真题

OFFICIAL37 What differences does the professor point out between sand particles and clay minerals? [Click on 2 answers.]

展开
Tip:单击查看句义;划选/双击查生词

[00:00.00]NARRATOR: Listen to part of a lecture in the geology class.[00:03.76]MALE PROFESSOR: So, we all know soil. [00:06.90]It's important to plant growth, right? [00:08.93]And we know that there're different types of soil in different places and that some soils are more fertile than others. [00:16.20]But what is soil? [00:18.23]And how's it formed?[00:19.54] Well, we're going to go into this in some depth, but for now let's just lay down the basics.
[00:25.55]Soil is composed of two kinds of material: inorganic material, basically small pieces of rock, and organic material, which is animal and plant matter.
[00:38.56]OK. So, what do you think?[00:40.96] If I mix bits of rock with composted vegetables, will I get soil?[00:45.92] The answer is no, because the formation of soil is a dynamic process. [00:52.30] It involves not only the initial inputs, the raw materials, but also the transformation of those materials, and the movement of some of the materials and the loss of others.[01:04.10]So, the inputs are bits of rock and organic matter.
[01:09.22]Now, the bits of rock—the inorganic input to soil?uh...they come from the breakdown of rocks on Earth's surface through a process called weathering.[01:19.99]Weathering can be either physical or chemical. [01:24.90]Physical weathering, uh...that's when exposure to the elements over time causes a rock to break up and eventually disintegrate. [01:33.36]Uh... of course, some rocks are more resistant to physical weathering than others. [01:38.90]If you think of the sand particles in soil, those are the result of physical weathering, and they have the same chemical composition as the original rock.
[01:48.51]Now, chemical weathering, uh... that's the chemical breakup of rocks.[01:54.68] It differs from physical weathering in that the chemical properties of the minerals are actually changed. [02:01.52]The clay minerals you find in soil are the result of chemical weathering. [02:06.43]Clay minerals are called secondary minerals, because their composition has been altered.[02:12.44]Okay. So we have weathered rock, which needs to be combined with organic matter.
[02:19.34]So what does the organic input consist of?
[02:23.07]It's the remains of plants and animals, but mostly plants. [02:28.61]Now, just as rocks are broken down by weathering, the animal and plant residues are broken down, too. [02:36.08]They're reduced to simple chemicals by microorganisms in a process called mineralization.[02:42.82]And just as some rocks are more resistant than others to weathering, the compounds found in the soil's organic input resist mineralization at different rates. [02:54.84]The compound cellulose is the major constituent of most plant tissue. [02:59.96] It mineralizes relatively quickly. [03:02.36] But there are woody substances in certain plants that strengthen the cell walls. [03:07.90] They are found in smaller concentrations and their mineralization can take several years.[03:13.70] Weathering and mineralization transform the inorganic and organic inputs in a number of ways. [03:22.74] And it's partly from these transformations that soil gets its unique properties.
[03:27.91]How does it work?
[03:29.50] Uh... take the dark brown color of soil. [03:32.43] After microorganisms have broken down the cellulose, we're left with two things: the microbe's waste and the more resistant plant material that microorganisms can't break down easily. [03:45.17] These materials ultimately get transformed into a new material called humus.[03:51.13] And when humus is combined with the clay minerals in soil, that's what gives soil its dark brown color. [03:59.23] So now, if we've got clay and humus, these transformed materials, and we mix them together, we've got something very close to soil.
[04:10.04]But soil isn't static, and there're still other processes that go into the formation of soil: the movement and loss of materials.[04:19.50]The soil in any location isn't a uniform mixture.[04:24.57]Its composition varies with depth. [04:27.60] You see, mineral and organic materials move through soil vertically.[04:32.61]Some materials move more easily than others. [04:35.77] Water carries the more mobile materials from the upper level of soil to the lower levels.[04:41.13]So the upper levels of the soil eventually get depleted of these materials, while the lower levels get enriched with them. [04:48.76]And that creates distinct layers of soil as far down as the rock underlying the soil. [04:55.39]And the materials that dissolve easily in water can get lost completely if the water carries them horizontally out of the soil and into rivers.
[05:05.40]Now, of course, new mineral and organic material will be deposited at the surface and become incorporated into the soil, but you see how the processes of movement and loss contribute to the formation of soil.

2.What differences does the professor point out between sand particles and clay minerals? [Click on 2 answers.]

你的答案:
正确答案:BD
题目解析:
 后才能查看题目解析,还没有账号? 马上注册
教授在说到无机物风化的时候举了两种风化,一种是physical的,一种是chemical的,physical的例子就是沙子,风化过程中成分不变;chemical的例子是clay minerals,它们的成分变化了。BD正确。AC未提及,不选。对应原文如下:Weathering can be either physical or chemical. Physical weathering, uh...that's when exposure to the elements over time causes a rock to break up and eventually disintegrate. Uh... of course, some rocks are more resistant to physical weathering than others. If you think of the sand particles in soil, those are the result of physical weathering, and they have the same chemical composition as the original rock. Now, chemical weathering, uh... that's the chemical breakup of rocks. It differs from physical weathering in that the chemical properties of the minerals are actually changed. The clay minerals you find in soil are the result of chemical weathering. Clay minerals are called secondary minerals, because their composition has been altered.

学习页面

Medi

terr

anean

加强 + 政府 + 名词后缀

加强的政府——管理

原文例句

加入生词

本文生词 0

色块区域是你收藏过的生词;

查询次数越多,颜色越深哦~

显示文中生词

登录后才能收藏生词哦,现在登录注册>

本文重点词 45

文中加粗单词为本文重点词;

根据词频与核心词范围精心挑选,托福考试必掌握词汇。

显示文中重点词
学习本文词汇

文中划选/双击的生词、加粗重点词已收纳至词盒

可随时点击词盒查看哦~

只有在词句精学模式下才能开启词盒功能哦~

我知道了

词盒
收藏
笔记
我的笔记
5000
保存
反馈