thE DirECt rEAson For spECiAlisAtion is ______.
A．thE DEvElopmEnt in CommuniCAtion
B．thE growth oF proFEssionAlisAtion
C．thE ExpAnsion oF sCiEntiFiC knowlEDgE
D．thE splitting oF ACADEmiC soCiEtiEs