GMAT Critical Reasoning (CR) | Birds have been said to be descended

Birds have been said to be descended from certain birdlike dinosaurspecies with which they share distinctive structural features. The fossilrecord,however,shows that thiscannotbeso,since therearebird fossilsmucholderthantheearliestbirdlikedinosaurfossilsthathavebeenfound.

Whichofthefollowingisanassumptiononwhichtheargumentrelies?

A) Thebirdlikedinosaurshavenodescendants.
B) There are no flightless dinosaur species that have the
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