关于 to be 和as 的用法。

very hard to determine the correctiveness of the choice based on such trifle difference of diction.  You'd better post your questions and choices and find out other mistakes that are more obvious.

think sb/sth to be 或者 think of sb/sth as 

另外就是，不定式有“过去不知道，现在才发现”的意味，讲科学发现的句子用to be很多

9.
                    Astronomers at the Palomar Observatory have discovered a distant supernova explosion, one that they believe is a type previously unknown to science.

(A)  that they believe is

(B)  that they believe it to be

(C)  they believe that it is of

(D)  they believe that is

(E)   they believe to be of

Choice E is best. The pronoun that in A and B should be deleted, since the pronoun one is sufficient to introduce the modifier and the sentence is more fluid without that. In B and C,
                it and that it are intrusive and ungrammatical: the idiom is "believe x to be y." In the context of this sentence, the infini­tive to be is more appropriate than the limited present-tense is in referring to an event that occurred long ago but has been discovered only recently. Finally, A, B, and D lack of and so illogically equate this particular explosion with the whole class of explosions to which it belongs: it is not a type but possibly one of a type.

14. Paleontologists believe that fragments of a primate
                jawbone unearthed in Burma and estimated
                    at 40 to 44 million years old provide evidence of a crucial step along the evolutionary path that led to human beings.

(A)  at 40 to 44 million years old provide evidence of

(B)   as being 40 to 44 million years old provides evidence of

(C)  that it is 40 to 44 million years old provides evidence of what was

(D)  to be 40 to 44 million years old provide evidence of

(E)   as 40 to 44 million years old provides evidence of what was

D, the best choice, correctly follows estimated with to be. The other choices present structures that are not idiomatic when used in conjunction with estimated. Choices B, C, and E all mismatch the singular verb provides with its plural subject, fragments, and in choices C and E, what was is unnecessary and wordy. In choice C, the use of the verb phrase estimated that it is produces an ungrammatical sentence.

49. The cameras of the Voyager II spacecraft detected six small, previously unseen moons circling Uranus, which doubles to twelve the number of satellites now known as orbiting the distant planet

(A)  which doubles to twelve the number of satellites now known as orbiting

(B)   doubling to twelve the number of satellites now known to orbit

(C)  which doubles to twelve the number of satellites now known in orbit around

(D)  doubling to twelve the number of satellites now
                known as orbiting

(E)   which doubles to twelve the number of satellites
                now known that orbit

The pronoun which should be used to refer to a previously mentioned noun, not to the idea expressed in an entire clause. In A, C, and E, which seems to refer to a vague concept invol­ving the detection of moons, but there is no specific noun, such as detection, to which it can refer. Also in E, the use of the phrasing the number... now known that orbit is ungrammatical and unclear. B and D use the correct participial form, doubling, to modify the preceding clause, but D, like A, uses known as orbiting rather than known to orbit, a phrase that is more idiomatic in context. B, therefore, is the best answer.