欢迎来到上海新航道官网!英语高能高分,就上新航道!

4008-125-888

首页>sat>阅读>正文
雅思托福SAT备考学习群 新航道雅思全真模考 2018春季班

sat阅读真题+答案+解析

今天上海新航道 小编为大家带来的是关于sat阅读的真题,本题是一道批判思维的选这题。

题目:

Plants, and all other living things, require nitrogen for growth; it is an essential component ofnucleic acids and proteins. Although air is mostly nitrogen, this gaseous form is inaccessible toplants and must be fixed into ammonium to render it biologically relevant. Soil bacteria calledrhizobia fix nitrogen, but to do this they must first take up residence inside the roots oflegumes like pea, alfalfa, clover, and soybean.

Soon after a legume begins to grow, rhizobia invade its root hairs and multiply, causing theplant to form specialized organs—nodules—that contain the proliferating bacteria. Thissymbiotic arrangement benefits both parties: legumes can thrive without nitrogen fertilizersonly if they have functional nitrogen-fixing nodules, while the bacteria receive the energyneeded to multiply and fix nitrogen from the plant. When the plant dies, the fixed nitrogen isreleased into the soil so other plants can use it. This process has significant implications foragriculture, as nitrogen is the most common nutrient deficient in the earth’s soil and, thus,the one most commonly supplied by chemical fertilizers.

Rhizobia are a diverse group taxonomically, genetically, and metabolically. They can be foundin distant genera. Their symbiotic trait appears to have arisen independently multiple times byhorizontal transfer of genes. However, it is not thought that this horizontal gene transferis sufficient to confer symbiosis, or to explain the biodiversity of rhizobia. There must beselective pressures preventing or permitting the expression of the acquired symbiosis trait andadaptive mechanisms to deal with these pressures. But neither the pressures nor themeasures taken to circumvent them are known.

What can reasonably be inferred about the fixed nitrogen released when a plant dies?

A.It is biologically insignificant because it reverts to its gaseous form.

B.It is not sufficient to maintain adequate nitrogen levels in soil.

C.It is less useful for other plants than the nitrogen found in chemical fertilizers.

D.It is not a consideration in farmers' decisions regarding agricultural practices.

上海新航道SAT培训班

答案:B

解析:

Choice B is the best answer. The author states that soil commonly is nitrogen-deficient andthat nitrogen is often supplied by fertilizers, even though the fixed nitrogen released whenlegume plants with nitrogen-fixing nodules die can be used by other plants. This suggests thatthe fixed nitrogen those legume plants release is not enough to supply all of the nitrogen thatis needed in soil; fertilizers are needed to address the remaining nitrogen deficiency.

上海sat'培训班

上海sat'培训班

上海sat'培训班

在线咨询

1分钟快速了解新航道

选择一个靠谱的机构进行培训,能够省心、省事,衡量一个好机构的标准在于从6个方面去了解
品牌、行业分析、师资、助教、高分案例、学员评价

前沿的出国课程体系

寒假课程看这里

新航道热门项目

一半学费,一倍效果,梯级课程循序渐进,满足不同英语水平学员的需求

  • 美国留学完美解决方案

    专业化语言培训+个性化留学申请+
    美国适应/预修课程
    咨询课程
  • 13周年,百万学员成功留学!

    腾飞专区,高分荣誉榜

    旗舰校区:上海市徐汇区裕德路126号
    电话:4008-125-888 传真:+021-61208858
    版权所有:新航道(北京)管理咨询有限公司 京IPC备05069206