题目

We can surely overcome these difficulties _,___ we are closely united. A. so far as               B. so long as              C. as soon as           D. as well as 答案：B（2007•乌兰察布）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．