题目

A terrible fever made Anne Sullivan nearly lose her eyesight in her childhood, and the doctors said she was a hopelessly mad girl. She had been   41   in the basement of a mental hospital (精神病医院) in Boston. Sometimes, little Annie   42   hit anyone who came near to her. She ignored everyone who appeared in front of her most of the time.        However, an old nurse   43   that little Annie had hope. She went to   44   little Annie every day. The child ignored her in most cases, but the old nurse   45   stopped seeing her every day in the basement. The如图，AM切⊙O于点A，BD⊥AM于点D，BD交⊙O于点C，OC平分∠AOB．则∠B等于    度．