Climate change is having an unexpected effect【小题1】the diets of grizzly bears,【小题2】could cause problems in the future. 

Grizzly bears on Kodiak Island【小题3】 (usual) eat salmon ( 鲑) at the beginning of the summer. When the elderberries ripen ( 变成熟) at the end of the summer, they eat berries instead.

Now, however, increasing temperatures mean the elderberries are ripening earlier. The bears have a(n) 【小题4】(choose)— berries or salmon. They leave the streams full of salmon and stay in the hills eating elderberries instead.

“It's as if breakfast and lunch【小题5】 (serve) at the same time and there is nothing 【小题6】 (eat) until dinner,” said Oregon State University biologist William Deacy. “You have to choose between breakfast and lunch because you can only eat so much at a time.”

Berries are【小题7】(high) in sugar than salmon. They contain less protein and are easier for the body to break down, and the bears are gaining weight as【小题8】result.

The change in the bears' diet is also affecting the Kodiak Island ecosystem (生态系统). Normally the bears kill 75 percent of the salmon at the beginning of the summer. Now there are more【小题9】(survive) salmon.The forests are suffering from the lack of nutrients normally【小题10】 (provide) by the dead salmon.

Global warming is pushing the number of polar bears to 【小题1】 (it) limit. According to a new study, they could have fewer than 100 years left before 【小题2】 (extinct).

Polar bears live 【小题3】 hunting seals in the Arctic Ocean, but as ice melts in that region, their habitat continues to shrink. Amounts measured at the end of the 1970s show sea ice that lasts for more than a year in the Arctic has decreased at a rate of 13% per decade.

Studies show that 【小题4】 (decline) sea ice will lead to a reduction in polar bears. They will be unable to bear the effects of climate change over the next several decades. The scientists believe polar bears will be 【小题5】 (thorough) wiped out by 2100.

“What we’ve shown 【小题6】 (be) that, first, we’ll lose the survival of bear cubs (幼熊). Although cubs will be born, the female bears won’t have enough body fat to produce milk 【小题7】 (bring) them along through the ice-free season,” said Dr. Steven Amstrup, chief scientist of Polar Bears International, to the BBC.

The study estimates that, even in a situation 【小题8】 countries achieve a moderate (适度的) reduction in greenhouse gases, several 【小题9】 (population) of polar bears will disappear. But Amstrup said, “We can make 【小题10】 difference if we have an urge to keep climate change little.”

Leaf-cutter ants are interesting. 【小题1】(look) for leaves, the larger ants usually go out in groups. They bite of bits of leaves and carry them back. Watching these ants march in single file, carrying leaves, is quite a sight. These ants can carry a leaf that 【小题2】 (weigh) 20 times more than they do. The leaves 【小题3】 (collect) by the ants are not for eating. They are brought back so fungus(真菌) can grow on them. The fungus is the food for the ants.