试题出自试卷《2010年华南师范大学考博英语真题》

The salmon is one of our most valuable fish. It offers us food, sport and profit. Every year commercial fishing （1）a harvest of over a billion pounds of salmon from the seA.Hundreds of thousands of salmon are caught each year by eager（2）fishers.
In autumn, the rivers of the Northwestern United States come（3）with salmon. The salmon have left the ocean and are（4）their yearly run up river to spawn. Yet today, there are far fewer salmon than（5）, because the salmon , （6）has suffered from many perils of the modern age.
Water pollution has killed many salmon by（7）them of oxygen. Over-fishing has further decreased their number. Dams has another（8），because they lock migration paths. Fish ladders,（9）stepped pools, have been built so that salmon can swim（10）over the dams. But young salmon swimming to the ocean have trouble（11）the ladders. Often they（12）their deaths over the dam or are killed in giant hydroelectric turbines.
（13）America will continue to have plenty of salmon, conservationists have planned several ways to（14）the salmon population. Conservation officials have had some success（15）salmon in hatcheries and stocking salmon rivers with them. Salmon are also being（16）into new areas. In 1996, hundreds of thousands of young Coho salmon were planted in streams off Lake Michigan. The adults were expected to migrate to the lake and（17）an undesirable fish. The Cohoes（18）so well on this kind of fish in Lake Michigan（19）Cohoes are being planted in other Great Lakes.
Thanks to the foresight and（20）of conservationists, the valuable salmon should be around American shores, rivers and lakes for a long time to come.