题目

John is expecting his mother and sister ________ (meet) him at the train station. 答案：【答案】to meet【解析】句意：约翰正等着他的母亲和妹妹到火车站接他。根据句中“is expecting”可知是缺动词不定式，作宾语补足语，故填to meet。如图，AB是⊙O的直径，AD是弦，∠A=22.5°，延长AB到点C，使得∠ACD=45°．（1）求证：CD是⊙O的切线．（2）若AB=2，求OC的长．