og 211

可以说是时间被建立么？

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

答案是b

the period has been established?对么

period是人为划分的，

such as

i established a period of netgame.

可以说establish a period么？我查了朗文没有划分什么的意思啊

请指教

就是比如说　某某人开创了一个时代。

而且，时代这个概念本身是人为划分出来的。