PT 61 S4 Q21

In modern deep-diving marine mammals, such as whales,the outer shell of ... ...

Which one of the following, if true, most weakens the argument?
(A) Some deep-diving marine species must surface after dives but do not have bones with porous outer shells.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Complete Section: LR-B, Oct. '10 LSAT (PT 61 Sec. 4)