下面是甲乙两公司职工工资情况统计表．

    Today is Tom's birthday. After school he walks past the shop on the street corner. He looks into the window. That pair of trainers(运动鞋) is still there. He really wants to have them.

    He is very sad and walks away. He knows his mother can't buy him anything, because his mother has no money. The trainers are too expensive. He doesn't go home at once , because his mother can notice（注意）his worry. So he goes to the park and sits on the grass. Then he sees a boy in a wheelchair(轮椅). He finds that the boy moves(移动) the wheels with his hands. Tom looks at him carefully. The boy has no feet. He looks at his own feet. "It's much better（更好）to be without shoes than (比) without feet." he thinks. There is no reason for him to feel so sorry and sad. He smiles and thinks he is happy.

根据短文内容，选择最佳答案

如图，点A，B，C是⊙O上的点，AO=AB，则∠ACB= ____度．