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
In an intact plant community, undisturbed by human intervention, the composition of a community is mainly a function of the clim
In an intact plant community, undisturbed by human intervention, the composition of a community is mainly a function of the clim
admin
2011-02-11
61
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.
Why are there problem weeds?
选项
A、Because they cannot be eradicated by herbicides.
B、Because all selective herbicides can encourage the growth of previously unimportant weeds by eliminating their competitors.
C、Because they were hardly considered before so that their seeds were not prevented from germinating.
D、Because they benefit greatly from the fertilizer applied to the farm land.
答案
D
解析
本题为细节判断题。原文的第三段告诉我们:所有选用的除草剂都只适用于一定的范围,它们往往能控制住最需要控制的野草,但并非所有。那些没被控制住的草便从庄稼和化肥中获得了新的生长空间。如果没有找到根除它们的除草剂的话,它们就会迅速蔓延开去。选项D与原文相符,为最佳答案。
转载请注明原文地址:https://kaotiyun.com/show/gleO777K
0
专业英语八级
相关试题推荐
Inplaceoftheking,twochiefexecutiveswerechosenannuallybythewholebodyofcitizens.Thesewereknownaspraetors,or
ClassicIntentionMovementInsocialsituations,theclassicIntentionMovementis"thechair-grasp".Hostandguesthaveb
By______wemeanthereisnologicalconnectionbetweenmeaningsandsounds.
DreamFunctionsDreamingisacommonphenomenon.Practicallyallpeopledream,althoughwhethertheycan【1】______themisa
Thesystemic-functionalgrammaroriginatedwith______.
Justafewweeksago,economistsandmarketanalystswereexpectingtheFederalReservetocutshort-terminterestratesonefin
Computerprogrammersoftenremarkthatcomputingmachines,withaperfectlackofdiscrimination,willdoanyfoolishthingthey
Professionalwomenwhoputcareersonholdforfamilyorotherreasonsearnispercentlessoncetheyreturntotheworkforce,a
A、sevenB、elevenC、fifteenD、seventeenD
A、noisynuisances.B、armsinvolvedinwars.C、anti-socialpipes.D、nationalinstruments.B新闻中提到250年前,风笛被作为战争武器而被禁止演奏。由此可见B为正确答案。
随机试题
________,是主体对艺术品的意象品鉴渐入佳境后,终于升华为对意境的感悟。
申请借用切片的患方人员,必须遵守的规定是
与义齿由前向后的斜向戴入方向优点无关的是A.顺应了牙齿向近中倾斜的状况B.可以争取磨牙基牙画出1类导线,因磨牙的固位力强,一般多为主基牙C.利用了部分远中基牙近中邻面的倒凹,可防止义齿的抬向脱位D.增强义齿的固位E.便于义齿的取戴
证券自营业务的禁止行为包括()
下列各项中,不属于有限责任公司监事会行使的职权是()。
数据库管理员希望对数据库进行性能优化,下列操作中行之有效的方法是()。
素有世界“音乐之都”美称的维也纳金色大厅第一次迎接的中国民族声乐的歌唱家是()。
下列生活方式不符合低碳经济要求的是()。
看过许多名人访谈,他们无不谈到过去某段时期的迷茫与困惑、低潮与失败。彼时,如果他们向命运低头,他们就是失败者。只有冷静下来,摆正心态,才有_______、赢取辉煌的可能。可见,平日的积累与锻炼固然重要,但关键时刻的_______与爆发力却能成就一个真正的王
如图所示,扇形的半径为12,圆心角为60°,O为扇形的内切圆圆心,则阴影部分的面积为[].
最新回复
(
0
)