首页
登录
职称英语
It is a common belief that sharp frosts color the autumn leaves. As a matter
It is a common belief that sharp frosts color the autumn leaves. As a matter
游客
2024-03-12
34
管理
问题
It is a common belief that sharp frosts color the autumn leaves. As a matter of fact, such frosts are far more likely to turn leaves black or dull brown than to give them the gorgeous tints we admire.
The coloring of the leaves in the fall is a chemical process that is favored by gradual cooling rather than sudden cold. It is not entirely confined to the autumn. Bright red and yellow leaves are often found on the swamp maple and other trees, even in summer.
Through the season of growth the leaves serve as food factories for the trees. In their tiny cells the carbon of the air is combined with materials brought up by the tree fluid from the roots to form the starch, sugar, and other substances by which the whole tree is fed. The food-making process is performed by sunshine with the aid of a substance called chlorophyll. Chlorophyll is a mixture of several pigments, or coloring matters. One of these is green, and gives the leaves their ordinary color. Another is yellow and is the same substance that, on account of its abundance in growing grass, makes butter particularly yellow in the spring.
When the cool weather sets in and the growth of vegetation slows down, the trees need less food and gradually suspend work in the leaf factories. Both the food and the chlorophyll in the leaves are drawn into the body of the tree and stored up for use in the spring. This transfer involves many chemical changes. One of them is the breaking up of the chlorophyll into the substances of which it is composed. The green pigment passes out of the leaves before the yellow. Thus yellow becomes one of the prevailing hues of the autumn foliage.
The reds, which also prevail in the autumn, do not come from the chlorophyll, but from pigments contained in the sap. Their appearance indicates an excess of sugar in the leaves, after the withdrawal of other materials. It is supposed, also, that the reddening of the leaves protects the food materials from the harmful effects of strong light during their passage into the tree. The same red coloring is seen in the buds of many plants in the spring, where it probably also serves a protective purpose. [br] Which of the following is a true statement about the coloring of leaves?
选项
A、Sudden cold turns leaves black or dull brown.
B、Leaves are colored by sudden change of temperature.
C、Bright-color leaves are seldom found in hot seasons.
D、Red is the main color of the autumn leaves.
答案
A
解析
首段提到的sharp frosts与选项A中的Sudden cold同义,选项A就是首段第2句前半部分的内容,为本题答案。
转载请注明原文地址:https://www.tihaiku.com/zcyy/3528910.html
相关试题推荐
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
Itisacommonbeliefthatsharpfrostscolortheautumnleaves.Asamatter
随机试题
()多媒体阅览室()外文原版区[br]()视听资料室()网上检索
HowmanyapartmentswillbebuiltinHarHoma?[originaltext]Israelhasanno
直肠癌结肠造口术后的护理措施正确的是()A.结肠造口开放前用无菌干纱布外敷造口
房地产转让时,法律规定应当签订书面转让合同,合同的内容由当事人协商拟定,一般应包
肠梗阻类型中最常见的是A.蛔虫性肠梗阻 B.粘连性肠梗阻 C.痉挛性肠梗阻
患者,男,33岁。开水烫伤4小时后来医院就诊。双手及膝下部位皮肤红肿,有大小不一
临床采集痰检查结核菌的意义,说法正确的是A.痰菌阴性即可排除肺结核 B.痰菌阴
商业银行的资本管理中,监管资本的含义有()。A.银行实际持有的总资本要求 B
某企业生产经营需要甲材料,年度采购总量为100000公斤,甲材料单价为780
建设工程施工过程中,对于有毒、有害物质超过国家标准的建筑材料和装修材料,应是()
最新回复
(
0
)