首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The cause of the decline of North Africa is popularly attributed to climatic changes, the theory being that the area became hott
The cause of the decline of North Africa is popularly attributed to climatic changes, the theory being that the area became hott
admin
2010-10-14
80
问题
The cause of the decline of North Africa is popularly attributed to climatic changes, the theory being that the area became hotter and drier and the people were forced to abandon a thriving civilization. However, some geologists, after carefully weighing the evidence, have challenged the conclusion that the climate has changed in any important way since Roman tithes. Although climatological factors may also have contributed, it was man who destroyed the balance of nature responsible for maintaining soil fertility and moisture.
Why is it that under certain circumstances, the plant cover is unable to regenerate itself, thus setting the stage for serious erosion(腐蚀)? To answer this question, let us take an extreme example, the destruction of tropical rain forests. In general, the equatorial(赤道附近的)soil is poor: forests can exist in these regions only because they are part of a balanced cycle. All that the forest produces is returned to the forest. The organic matter that falls from the trees constitutes the humus(腐殖土)that the forest requires. When people cut down all the trees to make room for crops, the soil is laid bare and, deprived of shade, heats up. An increase in soil temperature increases the rate of decomposition(分解)of organic matter. Organic nitrogen(氮)is converted into soluble ammonia(氨)and nitrates(硝酸盐), which the rains quickly leach(沥滤,溶滤)away. It has been calculated that a rise in temperature from 77 to 78.8 may increase the loss of nitrogen by fifteen to twenty pounds per acre per year. With the fertility of soil destroyed, an irreversible change from forest to desert can be initiated.
Increase in the temperature of tropical soil ______.
选项
A、might cause the overflow of flood
B、may lead to the loss of organic nitrogen in it
C、will produce a great deal of organic nitrogen
D、is harmless to the growth of rain forests
答案
B
解析
这三句话表明温度升高会导致大量有机氮的流失。选项B符合原文意思。
转载请注明原文地址:https://kaotiyun.com/show/Qzy7777K
0
大学英语四级
相关试题推荐
A、Britain.B、NewYork.C、India.D、Japan.D题目问根据这篇讲稿世界上哪个国家的城市人口最密集。文章最后提到了两个人口最为密集的城市——东京和横滨。这两个城市都位于日本,显然日本是城市人口最为密集的国家。
Inthe1960s,medicalresearchersThomasHolmesandRichardRahedevelopedachecklistofstressfulevents.Theyappreciatedthe
Whenwethinkofentrepreneurs,mostofusimagine【C1】______,successful,over-achieverslikeBillGatesofMicrosoft,RichardB
Whenwethinkofentrepreneurs,mostofusimagine【C1】______,successful,over-achieverslikeBillGatesofMicrosoft,RichardB
Whenwethinkofentrepreneurs,mostofusimagine【C1】______,successful,over-achieverslikeBillGatesofMicrosoft,RichardB
Althoughtheenjoymentofcolorisuniversalandcolortheoryhasallkindsofnamestoit,colorremainsaveryemotionalands
Longbusridesareliketelevisionshows.Theyhaveabeginning,amiddle,andanend-withcommercialsthrownineverythreeorfou
A、Thelossofnaturalhabitatformanyspecies.B、Lessspaceforbuildingnewhomes.C、Lesscarbondioxideandoxygen.D、Reduced
ImaginesendingelectronicmailtoyourfriendintheU.S.ordiscussingyourgardeningproblemwitha【B1】______inAustralia,or
Canmoneybuyhappiness?Yes,【S1】______theauthorsofanewstudy--butonlyuptoapoint.Psychologyhasshownthatricherpeop
随机试题
1948年3月,吉林省人民政府迁回吉林市。()
生态系统在结构上包括______、_______、_______、_______。
Thetimehascome______wecanmakeextensiveuseofnuclearenergy.
张先生,45岁。出现头痛、头晕、焦躁不安、心悸、气急、视力模糊、恶心呕吐,出现尿少。既往有高血压史,平时没有控制血压,现血压190/120mmHg:该病人可能出现了()。
患者,女,64岁。右上腹持续胀痛半月余,伴恶寒发热,恶心呕吐,便秘尿赤。检查:巩膜轻度黄染,右上腹压痛、轻度反跳痛,右上腹可触及边缘不清的压痛包块。舌红苔黄腻,脉弦数。其治法是
患者因左颈部神经鞘瘤复发而出现Horner征,说明肿瘤可能来源于或者压迫了
劳动关系转化为劳动法律关系后,若其运行出现障碍,如违约行为、侵权行为出现,则劳动法将对劳动法律关系继续进行调整,这是劳动法的(),其目的在于消除劳动法律关系运行的障碍,使其顺利运行。
步亭花园社区占地3700亩,现有小区居民13万人。为了响应我国社会主义市场经济条件下现代文明社区建设,步亭花园小区在建设之初就成立了社区服务中心,步亭花园社区开拓创新.建立了“建设、管理、服务”三位一体的社区管理模式。社区服务中心是在区政府指导下,履行政府
信仰乃道德之本,没有信仰的道德,是无源之水、无本之木。没有信仰的人是没有道德底线的;而一个人一旦没有了道德底线,那么法律对于他也是没有约束力的。法律、道德、信仰是社会和谐运行的基本保障,而信仰是社会和谐运行的基石。根据以上陈述,可以得出以下哪项?
AInthe1500s,civilunrestledBtothebreakupCofVietnamDforseveralsmallerstates.
最新回复
(
0
)