题目

 It wasn’t long _____the broken windows were repaired．      A． before      B． after           C． when         D． since 答案：A如图，已知AB是⊙O的直径，直线CD与⊙O相切于点C，AC平分∠DAB．（1）求证：AD⊥CD；（2）若AD=3，AC=，求AB的长．