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以下是引用GiGi在2003-12-23 1:53:00的发言：
be able to 為何後面不能用被動?
关于这个问题，OG里面最权威的解释是来自这个题：
243. Some scientists have been critical of the laboratory tests conducted by the Federal Drug Administration on the grounds that the amounts of suspected carcinogens fed to animals far exceeds those that humans could consume.
(A) far exceeds those that humans could consume
(B) exceeds by far those humans can consume
(C) far exceeds those humans are able to consume
(D) exceed by far those able to be consumed by humans（E）
(E) far exceed those that humans could consume
In D, the use of the passive voice in the phrase those able to be consumed by humans is unjustified, as it increases wordiness while stating the meaning less precisely: it is accurate to call humans “able,” but not to call those [amounts] “able.”
用able to be在大全里搜索，几乎所有的题目考察点和正确选项的特点都惊人的一致，感觉ETS好像认为be able to是一个主动性很强的词，该词的逻辑主语必须具有发出be able to 后动词的能力，如果是该动作的承受方则一般都改成了can/could。看完下面若干例子，相信以后不会再上ETS的当了，呵呵。
236. The Coast Guard is conducting tests to see whether pigeons can be trained to help find survivors of wrecks at sea.
(A) to see whether pigeons can be trained to help find
(B) to see whether pigeons can be trained as help to find
(C) to see if pigeons can be trained for helping to find
(D) that see if pigeons are able to be trained in helping to find（A）
(E) that see whether pigeons are able to be trained for help in finding
10. Climatic shifts are so gradual as to be indistinguishable at first from ordinary fluctuations in the weather.
(A) so gradual as to be indistinguishable
(B) so gradual they can be indistinguishable
(C) so gradual that they are unable to be distinguished
(D) gradual enough not to be distinguishable（A）
(E) gradual enough so that one cannot distinguish them
6. There is ample evidence, derived from the lore of traditional folk medicine, that naturally occurring antibiotics are usually able to be modified to make them a more effective drug.
(A) are usually able to be modified to make them a more effective drug.
(B) are usually able to be modified to make them more effective drugs
(C) are usually able to be modified, which makes them more effective drugs
(D) can usually be modified to make them a more effective drug（E）
(E) can usually be modified to make them more effective drugs
10. When Congress reconvenes, some newly elected members from rural states will try and establish tighter restrictions for the amount of grain farmers are to be allowed to grow and to encourage more aggressive sales of United States farm products overseas.
(A) and establish tighter restrictions for the amount of grain farmers are to be allowed to grow and to encourage
(B) and establish tighter restrictions on the amount of grain able to be grown by farmers and encouraging
(C) establishing tighter restrictions for the amount of grain farmers are allowed to grow and to encourage
(D) to establish tighter restrictions on the amount of grain capable of being grown by farmers and encouraging（E）
(E) to establish tighter restrictions on the amount of grain farmers will be allowed to grow and to encourage
210. If additional deposits of oil are found, it will expand the amount that can be used as fuel and reduce the price of oil, even if the deposits are not immediately tapped.
(A) it will expand the amount that can be used as fuel and reduce the price of oil
(B) the amount that is able to be used as fuel will expand and the price of oil be reduced
(C) it will cause an increase in the amount that is able to be used as fuel and a reduction in the price of oil
(D) the amount that can be used as fuel will increase and the price of oil will drop（D）
(E) it will increase the amount of oil that can be used as fuel and cause a drop in the price
正确的用法：主动态
985 Those who have visited the Grand Canyon have typically seen layers of sediment in the gaping canyon, with different colors that mark the passage of time like the rings in a tree trunk.
(A) seen layers of sediment in the gaping canyon, with different colors that mark
(B) see layers of sediment in the gaping canyon, whose different colors mark
(C) been seeing layers of sediment in the gaping canyon, whose different colors are markers of
(D) been able to see layers of sediment in the gaping canyon, with different colors marking（D）
(E) seen layers of sediment in the gaping canyon, marking by different colo
3. Because the financial review covered only the last few fiscal years, and therefore the investigators were unable to determine the extent to possible earlier overpayments.
(A) and therefore the investigators were unable to determine the extent to possible
(B) so therefore the investigators were not capable of determining the possible extent of
(C) therefore the investigators were unable to determine the possible extent of
(D) the investigators were not capable of determining the possible extent of（E）
(E) the investigators were unable to determine the extent of possible
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发表于 2003-12-19 07:07:00
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