题目如图,△ABC\triangle ABC△ABC的顶点AAA、BBB、CCC均在OOO上,若∠ABC+∠AOC=90∘\angle ABC+\angle AOC=90^{\circ}∠ABC+∠AOC=90∘,则∠ABC\angle ABC∠ABC的大小是（ ）A.30∘30^{\circ}30∘B.45∘45^{\circ}45∘C.60∘60^{\circ}60∘D.70∘70^{\circ}70∘知识点：圆周角定理I章节：图形的性质 / 圆
