非限制性定语从句

Believed to originate from a small area on their foreheads,elephants emit low-frequency sounds that may be used as a "secret language" to communicate with other members of the herd.fficeffice" />

(A) Believed to originate from a small area on their foreheads,elephants emit low-frequency sounds that may be used

(B) Elephants emit low-frequency sounds that are believed to originate from a small area on their foreheads, and they may use this

(C) Elephants emit low-frequency sounds,believed to originate from a small area on their foreheads,that they may use

(D) Originating,it is believed ,from a small area on their foreheads;elephants emit low-frequency sounds they may use

(E) Originating,it is believed,from a small area on their foreheads,low-frequency sounds are emitted by elephants that may be used


key is C


that之前明显有逗号，为什么？这是限制性还是非限制性定语从句，如何区分，that和which的使用如何决定？谢谢！

但是,OG11中有:

7. Carnivorous mammals can endure what would otherwise be lethal levels of body heat because they have a heat-exchange network, which kept the brain from getting too hot.

A. which kept

B. that keeps

C. which has kept

D. that has been keeping          （B）

E. having kept

The two underlined words contain two separate errors. The pronoun (which) introduces ***nonrestrictive*** clauses, which include information relevant but not critical to an understanding of the sentence. The pronoun (that) introduces a restrictive clause, which is critical to understanding the sentence because the clause defines its antecedent. Here, the clause following (which) defines heat-exchange network, so (that) must be used in place of (which). The use of the past tense (kept) is incorrect because a current situation is discussed; the present tense (keeps) is consistent with the other verbs in the sentense.

B Correct. (that) introduces a restrictive clause; (keeps) indicates a current situation and is consistent with the other verbs in the sentence.

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