共用题干 The Tough Grass That Sweetens Our LivesSugar cane was once a wild grass...

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问题共用题干 The Tough Grass That Sweetens Our Lives

Sugar cane was once a wild grass that grew in New Guinea and was used by local people for roofing their
houses and fencing their gardens. Gradually a different variety evolved which contained sucrose（蔗糖） and
was chewed on for its sweet taste.Over time,sugar cane became a highly valuable commercial plant,grown
throughout the world.___________(46)
Sugar became a vital ingredient in all kinds of things , from confectionery（糖果点心）to medicine,
and,as the demand for sugar grew,the industry became larger and more profitable.________(47)Many
crops withered（枯萎）and died,despite growers'attempts to save them,and there were fears that the
health of the plant would continue to deteriorate.
In the 1960s,scientists working in Barbados looked for ways to make the commercial species stronger
and more able to resist disease.They experimented with breeding programmes,mixing genes from the wild
species of sugar cane,which tends to be tougher,with genes from the more delicate,commercial type.
________(48)This sugar cane is not yet ready to be sold commercially,but when this happens,it is
expected to be incredibly profitable for the industry.
__________(49)Brazil,which produces one quarter of the world's sugar,has coordinated an interna-
tional project under Professor Paulo Arrudo of the Universidade Estaudual de Campinas in Sao Paulo.Teams
of experts have worked with him to discover more about which parts of the genetic structure of the plant are
important for the production of sugar and its overall health.
Despite all the research,however,we still do not fully understand how the genes act in sugar cane.
_________(50)This gene is particularly exciting because it makes the plant resistant to rust,a disease which
probably originated in India,but is now capable of infecting sugar cane across the world.Scientists believe
they will eventually be able to grow a plant which cannot be destroyed by rust.

选项 _________（49） A:Eventually,a commercial plant was developed which was 5 percent sweeter than before,but also much stronger and less likely to die from disease. B:Unfortunately,however,the plant started to become weaker and more prone to disease. C: One major gene has been identified by Dr Angelique D, Hont and her team in Montpelier, France. D:The majority of the world's sugar now comes from this particular commercial species. E:Sugar cane is now much more vigorous and the supply of sugar is therefore more guaranteed. F: Since the 1960s,scientists have been analysing the mysteries of the sugar cane'S genetic code.

答案 F

解析前一句话提到，甘蔗成了一种非常有价值的商业作物，在世界范围种植起来。因此这句话应该是讲种植甘蔗成了获得糖的主要来源。故选D。
前面一句说由于对糖需求的增加，种植甘蔗这一行业也得以壮大并且获利更多。后面一句提到，很多甘蔗作物枯萎并且死掉，尽管种植者试图去救治它们，大家还是担心甘蔗的健康状况会持续恶化。所以中间的句子应该是承接的转折句。故选B。
前面讲到，科学家们正在寻找一种能使商业型甘蔗更强壮、抗病性高的方法。他们实验把野生甘蔗的基因和商业用甘蔗的基因相结合。后面一句讲这种类型的甘蔗还没有开始商业化地出售。由此可知，中间的句子应该是讲将研发的这种商业型甘蔗的特点，故选A。
该句位于段首应该是主题句。根据后面的内容该段主要讲，巴西这个甘蔗生产大国和一位教授合作来研究在甘蔗的基因结构中，哪一部分对生产糖最重要以及它整体的健康状况。故选F，意思是“从二十世纪六十年代起，科学家们就开始分析甘蔗基因的神秘性。”
前一句讲，尽管做了这么多的研究，但是我们仍不清楚甘蔗的基因情况。后一句开头说“这一基因之所以独特地存在是因为······”，这里提到的这一基因（this gene）应该是新发现的，故选C。第6部分：完形填空

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