gmat_perfect wrote:Rock samples taken from the remains of an asteroid about twice the size of the 6-mile-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 3.47 billion 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

Again
1>Subject is samples, which is plural. Hence require 'have' and not 'has'.
2>IDIOM is "dated at"

Hence E.

The subject of 'to be dated' is 'Rock samples', so we must use a plural verb. That eliminates A and B.

The idiom 'dated at' is also tested.
Correct: Samples are dated at 3 billion years old.
Incorrect: Samples are dated to be 3 billion years old.
Incorrect: Samples are dated as being 3 billion years old.

This gets rid of A, C, and D. The OA is E.

A more detailed explanation is available as this is GMATPrep Question 2352. To practice similar questions in a timed drill, set topic='Idioms AND Subject Verb Agreements'and difficulty='400-500' in the Drill Generator.

-Patrick