题目内容
deposits of clay. Look at cuts where highways have been built to see exposed clay beds; or
look at a construction site, where pockets of clay may be exposed. Rivers also reveal clay
along their banks, and erosion on a hillside may make clay easily accessible.
(5) What is clay made oF The Earth's surface is basically rock, and it is this rock that
gradually decomposes into clay. Rain, streams, alternating freezing and thawing, roots of
trees and plants forcing their way into cracks, earthquakes, volcanic action, and glaciers-all
of these forces slowly break down the Earth's exposed rocky crust into smaller and smaller
pieces that eventually become clay.
(10) Rocks are composed of elements and compounds of elements. Feldspar, which is the
most abundant mineral on the Earth's surface, is basically made up of the oxides silica and
alumina combined with alkalies like potassium and some so-called impurities such as iron.
Feldspar is an essential component of granite rocks, and as such it is the basis of clay.
When it is wet, clay can be easily shaped to make a variety of useful objects, which can
(15) then be fired to varying degrees of hardness and covered with impermeable decorative
coatings of glasslike material called glaze. Just as volcanic action, with its intense heat,
fuses the elements in certain rocks into a glasslike rock called obsidian, so can we apply
heat to earthen materials and change them into a hard, dense material. Different clays need
different heat levels to fuse, and some, the low-fire clays, never become nonporous and
(20) watertight like highly fired stoneware. Each clay can stand only a certain amount of heat
without losing its shape throughsagging or melting. Variations of clay composition and the
temperatures at which they are fired account for the differences in texture and appearance
between a china teacup and an earthenware flowerpot.
The author's main point in paragraph 1 is that clay deposits
查看答案
搜索结果不匹配？点我反馈
更多问题
某房地产2002年的净收益为20万元，剩余经济寿命30年，报酬率为10%，折现率为 8%，则其客观市场现值为188.54万元。()
听力原文： Those who use solar energy help us save our precious fuel. As you know, our supplies of oil and gas are very limited. There is just not enough on hand to meet all our future energy needs. And when Mother Nature says that's all, that's all. The only way we can delay hearing those words is by starting to save energy now and by using other sources, such as the sun.
We won't have to worry about the sun's running out of energy for another several billion years or so. Besides being an endless source of energy, the use of the sun has other advantages as well. For example, the sun does not offer pollution as other energy sources.
Furthermore, owners of solar homes will have extra protection against rising fuel costs. They will also have some protection against fuel shortage. When utility costs go up, owners of solar homes won't have to face the burdens brought about by increased costs.
With all these good points, why don't we see more of solar power？ There are many reasons for this. The biggest reason is money. Until now, it was just not practical for a home owner to put in a solar unit. There were cheaper sources of energy around. Solar costs are starting to equal the costs of oil and electricity. And experts say that gas will triple in cost in the next few years. In fact, gas is in such short supply right now that, in some places, it is not sold to new customers. Some customers are even having their supplies cut back.
(33)
The passage intends to______.
A．metadataB．componentsC．modelsD．entities
微信支付 
支付宝支付