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?