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Question1: Just as on smoking, voices now come from many quarters insisting that the science about global warming is incomplete, that it's Ok to keep pouring fumes into the air until we know for sure. This is a dangerous game: by the 100 percent of the evidence is in, it may be too late. With the risks obvious and growing, a prudent people would take out an insurance policy now.

What does "in" mean here? Is it a adverb? Can a adverb serve as a predicative?

Question2: 

The explanation for insensitivity to smell seems to be that brain finds it 14___ to keep all smell receptors working all the time but can 15___ new receptors if necessary. This may 16___ explain why we are not usually sensitive to our own smells we simply do not need to be. We are not 17___ of the usual smell of our own house but we 18___ new smells when we visit someone else's. The brain finds it best to keep smell receptors 19___ for unfamiliar and emergency signals 20___ the smell of smoke, which might indicate the danger of fire.



15.[A]introduce summon [C]trigger [D]create



my answer is: C but the referance answer is D. I think it's wrong,what do you think?
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First: both questions are poorly written (or you have made some typing errors while copying them).

Q1-- The evidence is in. In is an adverb. Adverbs can serve as sentential adverbs with linking verbs: The book is on the table. The clause means 'the evidence has been received'.
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Q2-- We would have to know more about physiology to be sure of the correct answer, but I suppose that new receptors are not created-- and if so, certainly not by the brain. The brain, as the core of the central nervous system, is an activator/deactivator of other organs and processes-- it inhibits or triggers them.
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"but we can [trigger] new receptors if necessary." The word "new" is misleading here, and prompts you to say "create new receptors." "New" here simply means "different from the ones which are already on line, or currently activated."

I was always told that nerve cells don't reproduce themselves. That is, you're born with all the nerve cells you'll ever have. They can only repair and regenerate certain parts.

But new stem cell miracles are happening all the time.
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Comments  
sorry sir, but I can't find the errors, could you figure them out please?

And here are the whole texts:

Do you remember all those years when scientists argued that smoking would kill us but the doubters insisted that we didn't know for sure? That the evidence was inconclusive, the science uncertain? That the antismoking lobby was out to destroy our way of life and the government should stay out of the way? Lots of Americans bought that nonsense, and over three decades, some 10 million smokers went to early graves.

There are upsetting parallels today, as scientists in one wave after another try to awaken us to the growing threat of global warming. The latest was a panel from the National Academy of Sciences, enlisted by the White House, to tell us that the Earth's atmosphere is definitely warming and that the problem is largely man-made. The clear message is that we should get moving to protect ourselves. The president of the National Academy, Bruce Alberts, added this key point in the preface to the panel's report “Science never has all the answers .But science does provide us with the best available guide to the future, and it is critical that our nation and the world base important policies on the best judgments that science can provide concerning the future consequences of present actions.”

Just as on smoking, voices now come from many quarters insisting that the science about global warming is incomplete, that it's Ok to keep pouring fumes into the air until we know for sure. This is a dangerous game: by the 100 percent of the evidence is in, it may be too late. With the risks obvious and growing, a prudent people would take out an insurance policy now.

Fortunately, the White House is starting to pay attention. But it's obvious that a majority of the president's advisers still don't take global warming seriously. Instead of a plan of action, they continue to press for more research-a classic case of “paralysis by analysis”.

To serve as responsible stewards of the planet, we must press forward on deeper atmospheric and oceanic research but research alone is inadequate. If the Administration won't take the legislative initiative, Congress should help to begin fashioning conservation measures .A bill by Democratic Senator Robert Byrd of , which would offer financial incentives for private industry, is a promising start .Many see that the country is getting ready to build lots of new power plants to meet our energy needs. If we are ever going to protect the atmosphere, it is crucial that those new plants be environmentally sound.

No.2

The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, but this is largely because, unlike animals, we stand upright. This means that our noses are limited to perceiving those smells which float through the air, ignoring the majority of smells which stick to surfaces. In fact, though , we are extremely sensitive to smells, even if we do not generally realize it. Our noses are capable of detecting human smells even when these are diluted to far below one part in one million.

Strangely, some people find that they can smell one type of flower but not another, whereas others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate particular smell receptors in the nose. These receptors are the cells which sense smells and send messages to the brain. However, it has been found that even people insensitive to a certain smell at first can suddenly become sensitive to it when exposed to it often enough.
The explanation for insensitivity to smell seems to be that brain finds it inefficient to keep all smell receptors working all the time but can trigger new receptors if necessary. This may also explain why we are not usually sensitive to our own smells we simply do not need to be. We are not aware of the usual smell of our own house but we notice new smells when we visit someone else's. The brain finds it best to keep smell receptors available for unfamiliar and emergency signals such as the smell of smoke, which might indicate the danger of fire.

Thank you very much!
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