2. 考研
  3. A.than B.which C.contribute A.These nutrients can【T1】______to the breeding of the organisms B.more【T2】______2,600 square k

A.than B.which C.contribute A.These nutrients can【T1】______to the breeding of the organisms B.more【T2】______2,600 square k

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问题 A.than    B.which    C.contribute
A.These nutrients can【T1】______to the breeding of the organisms
B.more【T2】______2,600 square kilometers
C.【T3】______carry poisonous substances
    The term "red tide" applies to the discoloration of water that sometimes occurs in certain areas of the ocean or sea.Although the color is often red, it may also be shades of brown or yellow.The World Book Encyclopedia reports that "the discolored areas may range from less than a few square yards to【T4】______."
    What causes such discoloration? Red tides are generally caused by several species of single-celled organisms.These tiny organisms have hair-like projections which they use to propel themselves in water.There are about 2,000 varieties of these organisms, 30 of【T5】______.These minute organisms usually stay in warm waters with high content of salt.
    A red tide occurs when there is a sudden and rapid bloom of these organisms.The concentration of these organisms may swell to 50,000,000 per quart of water! Although scientists do not fully understand why this happens, it is known that these organisms accumulate when certain conditions simultaneously affect the water.These include abnormal weather, optimum temperatures, an oversupply of nutrients in the water, a generous amount of sunlight, and favorable water currents.When a heavy rainfall occurs, minerals and other nutrients are sometimes washed from the land into coastal water.【T6】______.The result? Red tides!
【T5】
选项
答案C
解析 空格所在句的意思为：大约有2 000种这样的生物，其中的30种携带有毒物质。这些微生物通常生活于含盐量高的温带水域。所以，C项“携带有毒物质”符合题意。所以，答案是C。
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