OG12 SC 140，遇到两个相反的标准答案，confusing!

chuRiver

书上的答案是E:have been dated at 3.47 billion years old and thus are
但是我在网上搜到Manhattan GMAT Forum里有人问了一个相似的题：
网址是          http://www.manhattangmat.com/forums/dated-at-vs-dated-to-be-t604.html
Remnants of a meteorite that exploded in Siberian sky and scattered over 400 square km in and around lake baikal has been dated to be 1.23 Billion years old and thus is evidence of the earliest known Meteor impact on earth.

A. has been dated to be 1.23 Billion years old and thus is
B. has been dated at 1.23 Billion years old and thus
C. have been dated to be 1.23 Billion years old and thus are
D. have been dated as being 1.23 Billion years old and thus
E. have been dated at 1.23 Billion years old and thus are

在这里答案是C。那个论坛里的人也很疑惑。
请问date to be与date at哪一个更idiomatic?

frankiesun

OG 12的答案是权威的答案

我认为date 的idio就是date at，跟着OG走。

FactOrFiction

我查了longman和webster，都没说date的用法，跟at还是to be.

我做的时候靠语感，觉得to be是不定式，表示目的和将来的含义居多，所以选了at.

neolqy

（ verb）1.WRITE DATE1[vn] to write or print the date on sth:
Thank you for your letter dated 24th March.
2.FIND AGE2[vn] to say when sth old existed or was made:
The skeleton has been dated at about 2 000 BC. 这是牛津词典上的解释（高阶第七版），date at大概表示估计，to be可能是表示日期是确定的吧

neolqy

Fossils of the arm of a sloth, found in Puerto Rico in 1991, have been dated at 34 million years old,
making the sloth the earliest known mammal on the Greater Antilles islands。这也是一道题，我感觉还是date at比较idiomatic，OG的解释（就是140题的解释）不是也说date at是表示estimation of time的idiomatic的表达吗？至于Manhattan Gmat上那个题可以用排除法做吧？？
个人意见呵呵