Seven species of carp(鲤鱼) native to Asia have been introduced into United States waters in recent decades, but it's four in particular－bighead, black, grass and silver－that worry ecologists, biologists, fishers and policymakers alike. Introduced in the southeast to help control weeds and parasites in aquaculture (水产养殖) operations, these fish soon spread up the Mississippi River system where they have been crowding out native fish populations not used to peting with such aggressive invaders. The carps' presence in such numbers is also harming water quality and killing off sensitive species.
Asian carp are strong to jump over barriers such as low dams. They lay hundreds of thousands of eggs at a time and spread into new habitat quickly and easily. Also, flooding has helped the fish expand into previously unattainable water bodies. And fishers using young carp as live bait have also helped the fish's spread, as they have boats going through locks up and down the Mississippi.
The federal government considers the Asian carps to be annoying species and encourages and supports “active control” by natural resources management agencies. Federal and state governments have spent millions in tax dollars to prevent the carp from making their way into the Great Lakes, but an underwater electric fence constructed to keep them out has not worked as well as hoped, and policymakers are reviewing other options now.
In the meantime, state and federal agencies are monitoring the Mississippi and its branches for Asian carp and testing various barrier technologies to prevent their further spread. For instance, the National Park Service is cooperating with the state of Minnesota's Department of Natural Resources to construct new dams that are high enough to prevent Asian carp from jumping over. The Asian Carp Regional Coordinating Committee has funded DNA monitoring in potentially affected water bodies whereby researchers can determine whether the troublesome fish are present just by the biological footprints they leave behind. Individuals can do their part by not transporting fish, bait or even water from one water body to another, and by emptying and washing boats before moving them between different water bodies.
【小题1】Asian carp have been introduced to the USA in order to .A．improve water qualityB．help sensitive speciesC．control the number of native fishesD．control the ecosystem in aquaculture【小题2】The measure to keep Asian carp out of the Great Lake but proved not good is .A．testing various barrier technologiesB．construction of an underwater electric fenceC．Emptying and washing boats before using them.D．monitoring the Mississippi and its branches for Asian carp【小题3】It is suggested from the passage that .A．aquaculture operations are dangerous to the water bodiesB．scientific technology is useless in preventing Asian carp spreadingC．both the state and the individuals can make efforts to keep out Asian carpD．Asian carp have successfully invaded the Mississippi and the Great LakesD
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(答案→)D
解析：
文章大意：为控制水产养殖的杂草和寄生虫，亚洲鲤鱼被引进到美国，结果引发了一场生物灾难。密西西比河水生物已崩溃，为防止它们进入五大湖，美国政府决定立即采取行动。
【小题1】D 细节理解题。由第一段第二句话“Introduced in the southeast to help control weeds and parasites in aquaculture (水产养殖) operations...”可知，引进亚洲鲤鱼的目的是控制水产养殖的杂草和寄生虫。
【小题2】B 细节理解题。由第三段最后一句话“Federal and state governments have spent millions in tax dollars to prevent the carp from making their way into the Great Lakes, but an underwater electric fence constructed to keep them out has not worked as well as hoped, and policymakers are reviewing other options now.”可知。
【小题3】C 推理判断题。由最后一段可知，各州政府和个人都在努力赶走亚洲鲤鱼。