Answer - Speciation
Reasoning - Pretty much what has happen was the two species has evolved over the course of evolution if you want to put it that way why the are incapable of breeding.
c, 22,800 (4 half lifes, 1/2, 1/4, 1/8, 1/16)
It has a d<span>ense cluster of lymphocytes and macrophages in the medulla? Hope this helps....</span>