OG211

211. The period when the great painted caves at Lascaux and Altamira were occupied by Upper Paleolithic people has been established by carbon-14 dating, but what is much more difficult to determine are the reason for their decoration, the use to which primitive people put the caves, and the meaning of the magnificently depicted animals.

(A)            has been established by carbon-14 dating, but what is much more difficult to determine are

(B)            has been established by carbon-14 dating, but what is much more difficult to determine is

(C)            have been established by carbon-14 dating, but what is much more difficult to determine is

(D)            have been established by carbon-14 dating, but what is much more difficult to determine are

(E)            are established by carbon-14 dating, but that which is much more difficult to determine is

Two instances of subject-verb agreement must be observed in this sentence: The period... has been established and what is much more difficult to determine... is. Both clauses have singular subjects and must have singular verbs. (what从句，ETS认为是单数，所以谓语用单数)WHAOnly B, the best choice, observes these requirements. （主谓一致）A incorrectly uses the plural form are in the second clause. Choices C and D incorrectly use the plural form have in the first clause, and D incorrectly uses are in the second clause as well. E incorrectly uses the plural form are in the first clause. Furthermore, because the date of the period in question was established before the writing of the sentence, the verb of that clause must be in theform (has been established).（Jnlvo：before the writing of the sentence对此句而言=before now. 所以present perfect form 。

Furthermore, because the date of the period in question was established before the writing of the sentence, the verb of that clause must be in theform (has been established).

确认时间是在写这个句子前 是过去的动作

但现在完成时 是过去的动作对现在的影响或持续到现在 这里如何能理解出这个动作会对现在有影响或持续呢

或者说用现在完成时unnecessary (ETS常用)

谢谢

我们可以用这个例子来区分现在完成时和一般现在时。

现在完成时对于不可延续的动作，表示过去的动作一直影响至今，而一般现在时对于不可延续的动作，表示动作发生在过去，和现在没有任何关系。

如此句，the period ... has been established和the period ... was established相比，前者暗示的是‘年代的确定结果至今没有被更改过，也即从年代最初被确定一直到现在大家还都认为当时的确定结果和现在的看法一致。’而后者一般过去时，则暗示‘年代的确定动作发生在过去某个时间，现在，这个确定结果可能和以前的一样，也可能早已被一个新的年代确定结果所替代’

我的问题 如何从句中体会出 the period ... has been established和the period ... was established相比，前者暗示的是‘年代的确定结果至今没有被更改过，也即从年代最初被确定一直到现在大家还都认为当时的确定结果和现在的看法一致。

从句中如何体会出来

是不是应该是一般过去时？

请教大家为什么在og213里面说现在完成时表示suggest that the situation is no longer the case.

213. The Federalist papers, a strong defense of the United States Constitution and important as a body of work in political science as well. represents the hand­iwork of three different authors.

(A)  and important as a body of work in political science as well, represents

(B)  as well as an important body of work in polit­ical science, represent

(C)  and also a body of work of importance in polit­ical science is representing

(D)  an important body of work in political science and has been representative of

(E)   and as political science an important body of work too, represent

Choices A, C, and D contain singular verbs that do not agree in number with the plural subject, papers. Furthermore, A violates parallelism by aligning the adjective important with the noun defense; C, employing the present progressive tense, wrongly suggests that the triple authorship of The Federalist papers is a developing situation rather than an accomplished fact; and D, employing the present perfect tense, suggests that the situation of triple authorship is no longer the case. D is also garbled syntactically because the conjunction and has been misplaced. In E, the wording is awkward. Choice B is best.

有哪位能讲讲 现在完成时、一般现在时、现在进行时使用时表达的不同意思啊？ 感谢了

知识点——主谓一致：what 从句做主语时，主句的谓语动词形式由后面的名词决定；如果what在what从句中做主语，它的谓语动词形式应该与主句的谓语动词形式保持一致。/主语从句做主语只有这个例外，其他的都用单数谓语。

哪为NN可以举例说明一下

顶； 谁来讲讲，举个例子吧 谢谢！