【单选题】
Red tides are a global {{U}} (74) {{/U}}. They have been observed on both theAtlantic and the Pacific coasts of the United States andCanadA、They have also {{U}} (75) {{/U}} in many other places. Though relatively few people are {{U}} (76) {{/U}} them, red tides are not new.
In the Philippines, a red tide was first seen in the province ofBataan in 1908. Since then, red tides have been seen in many other {{U}} (77) {{/U}}.A、Philippines red tide expert told us that" {{U}} (78) {{/U}} the fish kills, the Philippines has documented 1,926 cases of dead shellfish poisoning caused by red tides".
The term "red tide" {{U}} (79) {{/U}} 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 {{U}} (80) {{/U}} of brown or yellow. The WorldBookEncyclopedia reports that "the discolored areas may range from {{U}} (81) {{/U}} a few square yards to more than 2,600 square kilometers".
What causes such discoloration Red tides are generally caused by several {{U}} (82) {{/U}} of single-celled organisms. These tiny organisms have hair-like projections which they use to {{U}} (83) {{/U}} themselves in water. There are about 2,000 varieties of these organisms, 30 of which carry poisonous {{U}} (84) {{/U}}. These minute organisms usually stay in warm waters with high content of salt.
A、red tide occurs when there is a sudden and rapid {{U}} (85) {{/U}} of these organisms. The concentration of these organisms may {{U}} (86) {{/U}} to 50,000,000 per quart of water!Although scientists do not fully understand why this happens. It is known that these organisms {{U}} (87) {{/U}} when certain conditions simultaneously affect the water. These include abnormal weather, {{U}} (88) {{/U}} temperatures, an oversupply of nutrients in the water, a generous {{U}} (89) {{/U}} sunlight, and favorable water currents. When a heavy rainfall occurs, minerals and other nutrients are sometimes washed {{U}} (90) {{/U}} the land into coastal waters. These nutrients can contribute to the breeding of the organisms. The result Red tides!
B．amount of
C．way to
D．account for
网考网参考答案：B
网考网解析：
足够的阳光，B项符合题意。means of方法；way to方法；account for说明。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>
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