填空题

阅读下面这篇短文，短文后有2项测试任务：(1)第23～26题要求从所给的6个选项中为规定段每段选择1个正确的小标题；(2)第27～30题要求从所给的6个选项中选择4个正确选项，分别完成每个句子。
Ocean Ecosystem Endangered
1. Spanning the oceanic divide between the U.S. and Russia, it is one of the richest and most commercially productive marine environments on earth, teeming with pollack (保镖) and halibut, fur seals and Steller’s sea lions, horn puffins and murres. The seals and seabirds depend on catching fish, and so do humans. More than 2,000 boats from the U.S., Russia, Japan, Norway, China, Poland and the Koreas haul in an annual catch worth roughly $1 billion. The portion taken off the shores of Alaska alone amounts to one-half the sea life caught by commercial fishing vessels in U.S. waters.
2. But will the bounty (奖励) last Since the majority of the world’s fisheries are in a state of collages, as too many boats chase too few fish, conservationists fear the same fate for the Bering Sea, the last great refuge of marine abundance. Competition among countries for the rights to fish certain sectors of the sea is already fierce and could turn violent, as it has elsewhere in the world. The Russians have severely depleted (耗尽) fish stocks in their zone, and the international area open to all boats, called the Doughnut Hole, has been nearly stripped of commercial fish.
3. No species is more important to man and beast than Pollack, the No. 1 ingredient (成分) of frozen fish sticks and the fish items served by chains like Burger King and Long John Silver. Each year the Bering Sea yields two billion kg of this bottom—dwelling creature, making the Pollack business the biggest fish harvest in the world.
4. On the surface, that business is healthy: the Pollack catch has stayed near record levels. But signs of over fishing and an ailing ecosystem can be seem higher up in the food chain. The fur-seal population has not increased despite a long-standing ban on commercial hunting. The number of Steller’s sea lions, which feed mostly on Pollack, has plunged 80% since the 1970s, and seabirds such as the red-legged kittiwake are also in trouble.
5. Even if fishing is brought under control, the Bering Sea faces threats that originate thousands of miles away. Wind currents from industrial areas far to the south bring in pollutants like insecticides and heavy metals, which collect in the tissues of wildlife and the local Inuit people. At the same time the region has been warming up, and part of the reason may be the build-up of greenhouse gases in the atmosphere. Whatever the cause, sea ice has been retreating farther to the north, making life harder for polar bears and other ice-dwelling animals.
A. Other threats to the Bering sea
B. Pollack—the most important kind o fish
C. The problems many counties face
D. How to protect Bering sea
E. Over-fishing destroys the food chain
F. Why to control fishing
Paragraph 4 ______.