首页
登录
职称英语
In an intact plant community, undisturbed by human intervention, the compositi
In an intact plant community, undisturbed by human intervention, the compositi
游客
2023-12-16
43
管理
问题
In an intact plant community, undisturbed by human intervention, the composition of a community is mainly a function of the climate and the type of soil. Today, such original communities are very rare—they are practically limited to national parks and reservations.
Civilization has progressively transformed the conditions determining the composition of plant communities. For several thousand years vast areas of arable land have been hoed, ploughed, harrowed and grassland has been cut or grazed. During the last decades the use of chemical substances, such as fertilizers and most recently of weed killers (herbicides) has greatly influenced the composition of weed communities in farm land.
All selective herbicides have specific ranges of activity. They control the most important weeds but not all the plants of a community. The latter profit from the new free space and from the fertilizer as much as the crop does; hence they often spread rapidly and become weeds unless another herbicide for their eradication is found.
The soil contains enormous quantities of seeds of numerous specie—up to half a million per square meters according to scientific literature—that retain their ability to germinate for decades. Thus it may occur that weeds that were hardly noticed before emerge in masses after the elimination of their competitors. Hence, the knowledge of the composition of weed communities before selective weed killers are applied is not only of scientific interest since the plant species present in the soil in the form of seeds must be considered as potential weeds. For efficient control the identification of weeds at the seedling stage, i.e. at a time when they can still be controlled, is particularly necessary; for the choice of the appropriate herbicide depends on the composition of the weed community. [br] A knowledge of the composition of a weed community______.
选项
A、is essential to the efficient control of weeds
B、may lead us to be aware of the fact that the soil contains enormous quantities of seeds of numerous species
C、helps us to have a good idea of why seeds can lie dormant for years
D、provides us with the means to identify weeds at the seedling stage
答案
A
解析
本题为推断题。从原文第四段的第4行我们可以知道:在选择出的除草剂得到应用之前,有关草类种群的知识不仅仅属于科研范畴,因为以种子的形式出现在土壤中的植物都必须被视作潜在的野草。那也就是说有关草类种群的知识是有效地控制野草的关键。所以,A为最佳答案。
转载请注明原文地址:http://tihaiku.com/zcyy/3278166.html
相关试题推荐
TotheTunxisCommunityCollegeClassof2002,Ioffermycongratulations.
TotheTunxisCommunityCollegeClassof2002,Ioffermycongratulations.
Inadiagnosticsituation______existsidebysidethroughoutthecommunity.A、tw
Inanintactplantcommunity,undisturbedbyhumanintervention,thecompositi
Inanintactplantcommunity,undisturbedbyhumanintervention,thecompositi
SincejoiningtheEuropeanEconomicCommunityin______,Britainhasadoptedthe
Thecommunitycollegeisakindof______collegespopularin______tosatisfyth
CommunitycourtsandcommunityjusticeprevailedinEnglandatthetimeoft
CommunitycourtsandcommunityjusticeprevailedinEnglandatthetimeoft
Naturalhealersandevensegmentsoftheconventionalmedicalcommunityreco
随机试题
Forthispart,youareallowed30minutestowriteashortessayonthetopic
设(X1,X2,…,Xn)是抽自正态总体N(u,σ2)的一个容量为10的样本,
“政治家办报”这一思想,最早是由()明确提出的。A.马克思 B.列宁 C.毛
模拟信号u1(t)和u2(t)的幅值频谱分别如图(a)和图(b)所示,则( )
设计模式中的( )模式将对象组合成树形结构以表示“部分一整体”的层次结构,使得
血清钾的正常参考值范围为()。A.1.5~2.5mmol/L B.2.5~3
金鱼实际上是一类人工驯养的鲫鱼。大约2000年以前,中国的古人就开始养殖银鲫。作
举例说明如何为在幼儿园一日生活中实施"动静交替"的原则。(15分)
科学家曾经做了一个实验,让小鼠连续吃了几个星期的蛋糕、薯条,然后再来做学习和记忆
不得故意或无意地做出损害他人名誉或事务的事情属于FIDIC道德准则中()的内容。
最新回复
(
0
)