spECiAtion, ______, rEsults whEn An AnimAl populAtion BEComEs isolAtED By somE FACtor, usuAlly gEogrAphiC.
A．Form BiologiCAl spECiEs
B．BiologiCAl spECiEs ArE FormED
C．whiCh Forming BiologiCAl spECiEs
D．thE FormAtion oF BiologiCAl spECiEs