GMAT Sentence Correction (SC) | Re: One of the earliest known birds with a beak and contour feathers

One of the earliest known birds with a beak and contour feathers, Confuciusornis sanctus, with large clawlike "thumbs" on its wings, which probably helped them to climb up to a launching position for flight.

A. with large clawlike "thumbs" on its wings, which probably helpedthem to
B. with large clawlike "thumbs" ontheir wings, which probably helped it to
C. had large clawlike "thumbs" on its wings, which probably helpedthem
D. had large clawlike
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