看了以往的讨论都集中在that和现在分词orbiting做定语到底是限定还是非限定可是我觉得有点舍本逐末 我觉得从og的解释可以看出 Choice E, the best answer, avoids redundancy by using are rather than may be, employs the idiomatic phrase the interaction of, and expresses the relationship between the stars in a clear, concise way--two stars orbiting each other. 一上来就说e正确因为1.may与前面likely重复,2.词组the interaction of 3.two stars orbiting each other.是清晰简洁的表达..也就是说分词比定语从句做定语简洁 In A and B, the use of may be is redundant because the beginning phrase It seems likely that has already established a degree of uncertainty. In A, the phrase the interaction where two stars orbit each other is imprecise and illogical, suggesting that the interaction is a place where the orbiting occurs. In B, the phrase two stars that each orbit the other is both awkward and needlessly wordy. Choice C can be faulted because to form a passive construction, are should take a verb form such as caused rather than an adverb such as because.
Also, the phrase two stars that orbit each other illogically suggests that there are two particular stars causing all the phenomena in question, rather than various sets of stars in various locations.这里强调的,我觉得并不是分词非限定,分词在前面没有逗号的情况下都是限定的,(如果有非限定的情况请拿具体题目说服我)这里的区别是分词泛指所有那些互相绕着轨道转的星星,是限定修饰星星,因为所有星星中肯定有些两两绕着轨道转,可能有些谁都不绕就自己转,还有三个一起绕的. 而that orbit each other是特指所有互相绕着轨道转的一对一对星星中的两颗. 我这么说大家应该明白了吧? 天上所有two stars是全集把天上所有星星两两随机组成一组(包括各转各的,两两互转,一转二,二转一,一转三......) two stars orbiting each other 分词修饰指上述全集中所有两两互转的 two stars that orbit each other 定语从句指所有两两互转的星星中特定的两颗,具体两颗,逻辑不合理,特定两颗引起了那么多天文现象?
In D, the word where has no clear or logical referent, and each is orbiting the other is awkward and unnecessarily wordy; it could be replaced by the clearer and more concise orbiting each other. | 
