Questions 26 to 35 are based on the following passage.
You might think of your teeth as tools, like built-in knives and forks, but if they are mere tools, why do they feel pain and wouldn't it be better if they could just 26 under any condition? In spite of our 27 discomfort, it turns out there's a good reason our teeth are so sensitive. Tooth pain is a 28 mechanism that ensures when a tooth is being damaged we'll notice and do something about it.
If we eat something too hot or too cold, or if the tooth is worn down enough where the tissue 29 is exposed, all of those things cause pain, and then the pain causes the person not to use that tooth to try to protect it a little bit more. So it's really a protective mechanism more than anything else. If teeth didn't feel pain, we might 30 to use them in situations that damage them, and for humans, damaging 31 teeth is a problem because, unlike crocodiles, we can't 32 them.
Teeth have three layers, only one of which-the innermost layer of the tooth-can hurt, as that layer of the tooth 33 both blood vessels and nerves. Pain is the only feeling to which the nerves in that layer respond. Whereas people with tooth sensitivity may complain, for example, of tooth pain 34 by heat or cold, the nerves in the inner layer don't sense temperature. Rather, they feel pain, which may be 35 with, say, drinking something very cold.
A) adult I) emotional
B) associated J) implies
C) chew K) mammal
D) contains L) replace
E) continue M) swallow
F) defense N) triggered
G) dental O) underneath
H) downward
答案解析：
26. 根据“why do they feel pain and wouldn't it be better if they could just...under any condition”，结合语境可知这里说如果牙齿在任何条件下都能“咀嚼”就好了，continue不符合语境，chew“咀嚼”合适，所以选C。
27. 根据“it turns out there's a good reason our teeth are so sensitive”以及前面说牙齿像工具却会疼，可知这里说的是尽管我们有“牙齿方面的”不适，dental“牙齿的”符合，所以选G。
28. 根据“ensures when a tooth is being damaged we'll notice and do something about it”可知牙疼是一种“防御”机制，defense“防御”符合，所以选F。
29. 根据“is exposed”以及常识可知是牙齿组织“下面的”暴露了，underneath“在……下面”符合，所以选O。
30. 根据“If teeth didn't feel pain”可知如果没有痛感，我们可能会“继续”在损害它们的情况下使用牙齿，continue“继续”符合，所以选E。
31. 根据“for humans”可知这里说的是损害“成年人的”牙齿是个问题，adult“成年人的”符合，所以选A。
32. 根据“unlike crocodiles”可知鳄鱼可以“更换”牙齿，而人类不能，replace“更换”符合，所以选L。
33. 根据“both blood vessels and nerves”可知牙齿最内层“包含”血管和神经，contains“包含”符合，所以选D。
34. 根据“by heat or cold”可知这里说的是由冷热“引发”的牙疼，triggered“引发”符合，所以选N。
35. 根据“with, say, drinking something very cold”可知这里说的是疼痛可能与喝很冷的东西“有关”，be associated with“与……有关”符合，所以选B。
