GMAT Sentence Correction (SC) | Re: Rock samples taken from the remains of an asteroid about twice the siz

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 thusis - "has been " does not work with plural "rock samples"
(B) has been dated at 3.47 billion years old and thus - "has been " does not work with plural "rock samples"
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