因为AB=AC所以角A=180-72-72=36度角BOC=90+1/2角A=108度角DOB=180-角BOC=72度选C
∵AB=AC∴∠ABC=∠ACB=72°∵CD平分∠ACB，OB平分∠ABC∴∠OBC=1/2∠ABC=36°，∠OCB=1/2∠ACB=36°∴∠DOB=∠OBC+∠OCB=36°+36°=72°选C
