whAt is thE mAin topiC oF thE pAssAgE
A．thE wAys in whiCh Crows DiFFEr From othEr Common BirDs.
B．thE myths AnD lEgEnDs ABout Crows.
C．thE ChArACtEristiCs thAt mAkE Crows DiFFiCult to stuDy.
D．thE Existing mEthoDs For invEstigAting Crow BEhAvior.