The Convergence in External Morphology of Sharks,penguins,and Porpoises Is Attributed

Multiple Choice

The convergence in external morphology of sharks,penguins,and porpoises is attributed to  

A) reduced genetic variability in these groups.
B) selection pressures that are common to these groups.
C) reproductive isolation of these groups.
D) identical genes in all three groups.
E) use and disuse of the limbs.