Below America‘s waters,there is a junkyard(垃圾场).Every year, thousands of boats and ships sink or are abandoned in the U.S.and most of them are never found back again.’You go to any harbor in the country and you‘ll find abandoned ships,’ said Doug Helton, Director of the National Oceanic and Atmospheric Administration (NOAA). NOAA data suggests there are at least 10,000 abandoned ships along the U.S. coast, but experts predict there can be far more.Abandoned ships damage the ecosystem(生态系统）long after they‘ve sunk. They produce toxic chemicals harming or destroying sea life and, by entering the food chain, the chemicals are finally digested by humans. Sometimes they help the growth of new sea life that threatens the present local ecosystem. On Palmyra Atoll, for example, a ‘population explosion’ of corallimorph, an aggressive creature similar to coral, killed almost all the coral growing around a fishing boat that sank in 1991. The corallimorph were probably attracted to the leaching iron produced by the abandoned boat, growing fast and threatening other sea life on the reef.Of course, there are governmental policies to prevent people from abandoning boats and ships. State laws fine (罚款) and sometimes jail those irresponsible ship owners. However, there’s a big financial problem regarding retrieving(回收）and recycling sunken ship: it takes owners on average $5,000 to $10,000 to retrieve a 40-foot yacht, while the fines for abandonment are much lower - only $100. Besides, definitions of ‘abandonment’ are quite different among states, which means that ship owners can sometimes sink boats and get off the responsibility. Meanwhile, federal law deals with only pollution caused by ships, not with ship abandonment itself.The environmental impact of undersea boats and ships can’t always be seen easily from the shore, says Helton. It would help if owners of small fishing boats as well as big ships could keep in mind that ‘ when a boat or ship is lost, it’s not gone.1.The main idea of the passage is（）.A、poisonous chemicals‘ influences on sea lifeB、policies of retrieving abandoned shipsC、how corallimorph threatens coralD、the sunken ships and its trouble2. According to the passage, abandoned ships damage the ecosystem in these ways EXCEPT（）.A、producing toxic chemicalsB、entering the food chainC、helping corallimorph growD、poisoning the fishing boat3.The example of corallimorph is to show how abandoned ships（）.A、produce toxic chemicals which harm sea lifeB、foster new sea life threatening the ecosystemC、are protected under governmental policiesD、are retrieved and recycled in cheaper ways4.The third paragraph implies that（）.A、The fact that sunk ships can never be repaired.B、There are no financial problems of retrieving sunken ships.C、It doesn’t matter if we don’ t have a common definition of ‘abandonment’.D、Federal laws concerned only with pollution.5.The Helton‘ s attitude to lost ships is（）.A、indifferentB、disapprovingC、supportiveD、worried