Section B
Directions: In this section, you will hear 3 short passages. At the end of each passage, you will hear some questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A, B, C and D.
听力原文: A deadly infectious outbreak swept through a small city in Zaire, Africa last spring, killing more than one hundred people. The killer was a rare virus that caused most victims to bleed to death. As scientists rushed to control the outbreak, people in the U.S. wondered "Could it attack here." "We are foolish if we think it couldn't come to our country," say doctors. The virus can be highly infectious. If you come in contact with a victim' s blood or other body fluids, you can get
sick, too. All it takes is one infected person to start such a disease. That' s what scientists believe happened in Zaire. The healthcare workers who treated the first victims there soon fell ill too. The problem was: they had no protective equipment to prevent themselves from being infected. International rescue workers brought equipment to Zaire soon after the out- break occurred. Now the disease appears to be under control. One big mystery is that no one knows where the virus comes from or where it will strike next. Some scientists say that the virus lies inactive in the cells of some kind of plant, insect or other animals, Then it somehow finds a way to infect humans. Scientists are now headed into the jungles of Africa to find out where the virus lives. Once they find the virus, they also hope to find ways to combat it.
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A. Through food.
B. Through air.
C. Through insects.
D. Though body fluids.
下列选项中,关于铸铁说法错误的是()。A.铸铁是铁合金的一种,与钢相比,其成分特点是碳、硅含量高,杂下列选项中,关于铸铁说法错误的是()。
A. 铸铁是铁合金的一种,与钢相比,其成分特点是碳、硅含量高,杂质含量也较高
B. 杂质在钢和铸铁中的作用完全不同,如磷在耐磨磷铸铁中是提高其耐磨性的主要合金元素,锰、硅都是铸铁中的重要元素,唯一有害的元素是硫,铸铁的组织特点是含有石墨,组织的其余部分相当于碳的质量分数小于0.80%钢的组织
C. 铸铁的韧性和塑性,主要决定于石墨的数量、形状、大小和分布,其中石墨形状的影响最大
D. 按照铸铁成分中是否含有合金元素,可分为一般铸铁和合金铸铁两大类。一般铸铁可分为普通铸铁和变质铸铁