题目选项分析

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

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