题目内容：

    Rescue workers had collected 820 birds from the Gulf of Mexico oil spill, the majority of them already dead. The current spill promises to be the largest in US history, and as cleanup efforts stretch across the summer, it's clear that more oiled birds will be found, stuck and suffering in the black stick liquid. And as they do with every oil spill, rescue workers will go to great lengths to capture and clean the survivors hoping to restore them to their natural habitat.

Is it worth the effort? Some scientists aren’t so sure. Because the stress of being captured and bathed is as significant as the horror of being immersed in oil, and because research suggests that many rescued birds die shortly after being released, some experts say euthanasia (安乐死) is a more humane option.

Clean bird feathers repel water (防水) and regulate body temperature while dirty ones don't. Oil in particular makes feathers heavier and decreases their ability to trap air, which in turn makes birds weak and become easier to drowning, overheating and organ damage. Of course, being captured and cleaned is no picnic either. Some birds wind up returning to their destroyed habitats only to fall victim to the oil again. And those who manage to avoid a second oil bath suffer dramatically shortened life spans (跨度) and lower reproductive success. Of the thousands of birds that were rescued from the Prestige oil spill off the coast of Spain in 2002, only 600 were released into the wild; most of the rest died after just a few days in captivity.

However, bird rescuers say they have learned a lot about how to best help oil-soaked birds, and that therefore, survival rates stand to increase this time around. In the past, birds were cleaned right away, and volunteers often worked through the night bathing rescued birds. But now, captured birds are left to rest for a day or two before being cleaned, and only washed during the day, so as not to disrupt their circadian (生理的) rhythms. But part of that increase may be due to greater selectivity on the part of rescuers. The workers do blood tests right in the field now and birds that are loaded with hydrocarbons (碳氢化合物) or don’t look like they’re going to make it are put down right away, rather than subjected to the stress of captivity and cleaning.

And so far, while release rates may be improving, there is little evidence of better medium or long-term survival, especially for the more-difficult-to-save species. There still aren’t good protocols (协议) for repairing the internal organ damage. Anyway, rescue efforts will continue in large part because the public demands that. Euthanasia is a difficult thing to do, especially for people who have built their lives around saving animals.

1.Why do some scientists doubt the effort to rescue oiled birds?

A.Because it has cost too much time and money.

B.Because human may be infected with the bird virus.

C.Because it is torture followed by death to birds.

D.Because migrant birds may broaden the pollution.

2.The case of Spain coast spill is mentioned to indicate ________.

A.thousands of birds were polluted by oil

B.the survival rate of oiled birds was very low

C.the efforts to rescue oiled birds were ineffective

D.captivity is an impractical method to rescue binds

3.Why do the survival rates of oiled birds increase?

A.Oiled birds are kept in warm water for one or two days

B.The second cleaning of the oiled birds in daytime is not permitted

C.The rescuers often select the birds that are likely to survive

D.Hydrocarbons are removed to rescue the oiled birds

4.Why does oiled birds' rescue remain a controversial problem?

A.Oiled birds’ internal organ damage is permanent.

B.Euthanasia is a difficult and heart-aching operation.

C.The more-difficult-to-save species will die by cleaning.

D.The rescue is oiled birds’ suffering while seeing them die is cruel.