Why do some biologists NOT consider reptiles to be a monophyletic group?

A) Birds are the direct descendants of some reptiles.
B) Reptiles evolved independently at several different times in the past and from several different ancestral species.
C) Reptiles, birds, amphibians, and fish appeared in the fossil record at approximately the same time.
D) All reptiles do not reproduce sexually.
E) The ancestors of reptiles are the class Amphibia.