2. 考研
  3. A. which B. than C. to Phrases: A.【T7】______carry poisonous substances B. more【T8】______2,600 square kilometers C. These nutri

A. which B. than C. to Phrases: A.【T7】______carry poisonous substances B. more【T8】______2,600 square kilometers C. These nutri

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问题 A. which
B. than
C. to
Phrases:
A.【T7】______carry poisonous substances
B. more【T8】______2,600 square kilometers
C. These nutrients can contribute【T9】______the breeding of the organisms
    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【T10】______"
    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【T11】______. 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.【T12】______. The result? Red tides!
【T11】
选项 A、 
B、 
C、 
答案A
解析 空格所在句的意思为：大约有2 000种这样的生物，其中有30种携带有毒物质。A项符合上下文。
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