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Model Test 4The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, 1__ this is largely because, 2 animals, we stand upright. This means that our noses are 3__ to perceiving those smells which float through the air, 4 the majority of smells which stick to surfaces. In fact, __5__, we are extremely sensitive to smells, 6__ we do not generally realize it. Our noses are capable of 7__ human smells even when these are 8__ to far below one part in one million.Strangely, some people find that they can smell one type of flower but not another, _9_ others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate _10_ smell receptors in the nose. These receptors are the cells which sense smells and send 11 to the brain. However, it has been found that even people insensitive to a certain smell 12 __ can suddenly become sensitive to it when 13__ to it often enough. The explanation for insensitivity to smell seems to be that the 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. 1. A) although B) as C) but D) while 2. A) above B) unlike C) excluding D) besides 3. A) limited B) committed C) dedicated D) confined4. A) catching B) ignoring C) missing D) tracking5. A) anyway B) though C) instead D) therefore 6. A) even if B) if only C) only if D) as if 7. A) distinguishing B) discovering C) determining D) detecting8. A) diluted B) dissolved C) dispersed D) diffused 9. A) when B) since C) for D) whereas 10. A) unusual B) particular C) unique D) typical 11. A) signs B) stimuli C) messages D) impulses 12. A) at first B) at all C) at large D) at times 13. A) subjected B) left C) drawn D) exposed 14. A) ineffective B) incompetent C) inefficient D) insufficient 15. A) introduce B) summon C) trigger D) create16. A) still B) also C) otherwise D) nevertheless 17. A) sure B) sick C) aware D) tired 18. A) tolerate B) repel C) neglect D) notice 19. A) available B)reliable C) identifiable D) suitable 20. A) similar to B) such as C) along with D) aside from 1. C) 2. B) 3. A) 4. C) 5. B) 6. A) 7. D) 8. A) 9. D) 10. B) 11. C) 12. A) 13. D) 14. C) 15. D) 16. B) 17. C) 18. D) 19. A) 20. B)
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