（1）     GWD-31-Q28?????????

Rock samples taken from the remains of an asteroid about twice the size of the 6-nuke-wide asteroid that eradicated the dinosaurs has been dated to be 3.47 billion years old and thus is evidence of the earliest known asteroid impact on Earth.

A: has been dated to be 3.47 billion years old and thus is

B: has been dated at 3.47 billion years old and thus

C: have been dated to be 3.47billion years old and thus are

D: have been dated as being 3.47 billion years old and thus

E: have been dated at 3.47 billion years old and thus are

C the best 

 看讨论 到底是C 还是E啊    

 为甚么thus are  前面不是have been 吗？？？？？ 

E

可參考GWD-8-34
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.

结构： the remains of X have been dated at... and thus are evidence of....

C和E语法上讲都是对的，只能说ETS更喜欢E的用法，而且确实E 中，
                dated at n years old
                是更常见的用法。Nytimes上无数

也是GWD的题：Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles islands.
            

虽然也能找到2，3个dated to be的例子，但是的确比较少用

http://www.nytimes.com/2007/12/09/world/europe/09cave.html?ref=todayspaper&pagewanted=all

But its images, dated to be 30000 years old, and its floor, dotted with ancient footprints of people and animals, have been open only to researchers and

An episode this season also revealed that a crashed alien spaceship, carbon-dated to be millions of years old, was encrypted with passages from the world's

正规常用的是 date back to, date from, date at