不定式总结
748. The fear of rabies is well founded: few people are known to recover from the disease after the appearance of the clinical symptoms.
(A) few people are known to recover from the disease after the appearance of the clinical symptoms
(B) few people are known to have recovered from the disease once the clinical symptoms have appeared
(C) there are few known people who have recovered from the disease once the clinical symptoms have appeared
(D) after the clinical symptoms appear, there are few known people who have recovered from the disease (B)
(E) recovery from the disease is known for only a few people after the clinical symptoms appear
Choice A does not clarify the timing of events but rather suggests that a few people continue to recover indefinitely. In B, the best choice, have recovered and have appeared indicate that the action of recovery is completed rather than ongoing. In choice C, the impersonal construction (there are) is needlessly wordy; moreover, the placement of known wrongly implies that the issue is whether the people rather than the instances of recovery are known. Choice D further confuses matters by placing the after phrase well before recovered, the verb it modifies. Choice E is indirect and unidiomatic. The question is of average difficult.
Be known to do （朗文：Smoking is known to increase a person's risk of developing lung cancer.）
强调了康复和症状显现都是已经完成的动作，用完成是强调了这个完成的动作的影响。
849. (section B 14)
The Western world’s love affair with chocolate is well-documented: few people have been known to have tasted it for the first time without requesting more.
(A) few people have been known to have tasted it
(B) few having been known to taste it
(C) it has been tasted by few people
(D) few people have been known to taste it
(E) few people having tasted it
Be known to do sth
Be known to do sth
本题强调很少人被知道，用了完成时。但是taste是不是可以用在完成时中，是值得讨论的。（请赐教）
牛津高阶:
牛津高阶:
牛津高阶:
[VN] to eat or drink food or liquid: I've never tasted anything like it.
have short experience
[VN] to have a short experience of sth, especially sth that you want more of: He had tasted freedom only to lose it again.
如果从强调的角度来说，强调的是很少有人知道，而不是尝巧克力，那么后者就不需要用完成时态了。
如果从强调的角度来说，强调的是很少有人知道，而不是尝巧克力，那么后者就不需要用完成时态了。
19. The herbicide Oryzalin was still being produced in 1979, three years after the wives of workers producing the chemical in Rensselaer, New York, were found to have borne children with heart defects or miscarriages, and none of their pregnancies was normal.
(A) to have borne children with heart defects or miscarriages, and none of their pregnancies was
(B) to have had children born with heart defects or miscarriages, and none of the pregnancies was
(C) either to have had children with heart defects or miscarriages, without any of their pregnancies being
(D) either to have had miscarriages or to have borne children with heart defects; none of the pregnancies was（D）
(E) either to have had miscarriages or children born with heart defects, without any of their pregnancies being
Choices A and B are incorrect because with governs both heart defects and miscarriages; in other word, choice A says that the children and not the women suffered the miscarriages. For the sentence to make sense, miscarriages must be the object of a verb that has wives as its subject. Also, their in choices A, C, and E is ambiguous because it is far from its referent, wives. Choices C and E lack parallel construction: a verb form like the one after either should appear after or. Choice D is the best answer for this difficult question.
Be found to do sth（朗文：The liquid was found to contain 7.4g of phenylamine）
答案用了排除法，根据平行对称的原则和没有歧义的原则，对于不定式的时态没有详细的解说。但是个人认为had miscarriages和borne children with heart defects是发生在found之前的，所以用了完成时态，和gemj大牛的看法一样。而且miscarriages和borne children with heart defects是可以延续的，用在完成时中没有问题。
再从强调的角度来看，个人感觉不太出来是都想强调，还是强调其中一者，被发现，还是发现流产和有病，都说的过去，请教大牛们~
325. Geologists believe that the Bering land bridge, over which human beings are thought to have first entered the Americans, disappeared about 14,000 years ago when massive glaciers melted and caused the sea level to rise several hundred feet worldwide.
(A) are thought to have first entered
(B) were thought first to enter
(C) were thought at first to enter
(D) are thought of as first entering(A)
(E) were thought to first enter
Be thought to do sth
Have entered是在thought之前的，所以用了完成时态，are和前面的 believe时态一致，没有问题。
sectionB-19
sectionB-19
Balzac drank more than fifty cups of coffee a day and died of caffeine poisoning; furthermore, caffeine did not seem to bother Samuel Johnson, the great writer and lexicographer, who was reported to have drunk twenty-five cups of tea at one sitting.
(A) furthermore, caffeine did not seem to bother
(B) however, caffeine did not seem to bother
(C) however, caffeine did not seem to have bothered
(D) furthermore, caffeine did not seem to have bothered(B)
(E) in addition, caffeine did not seem to bother
Seem to do sth
个人觉得这个是seem to do的固定用法。如果按照jonasjin的说法“但这里因为seem 不是表达别人意见的词，而是做着对这件事情的看法，所以就没有必要用to have bothered ”感觉很有道理，我想补充的一点是，咖啡因有没有bother SJ是在was reported之后得出的结论，或者是在was reported的同时被人们发现的，所以就没用完成时。
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