如图，AB是⊙O的直径，C是⊙O上一点，AD垂直于过点C的直线，垂足为D，且AC平分∠BAD．

(1)求证：CD是⊙O的切线；
(2)若AC＝2$\sqrt{6}$，AD＝4，求AB的长．

阅读下列短文，根据短文内容填写表格。(每空限填一词)     

    Hi! Do you know the three children? They are in a happy family. Xiao Xue is a helpful girl. She is beautiful. She likes studying. She studies very hard. She gets up early and finishes her breakfast quickly .Then she rides her bike to school . Liu Xing is a little lazy. He gets up late and then washes his face, brushes his teeth in a hurry. Then he goes to the bus stop without breakfast. He usually plays basketball after school. In the evening, he seldom (很少)does homework. He goes to bed late. Xiao Yu is a lovely boy. He gets up very slowly and then he usually takes a shower(淋浴)at home before breakfast. After that, he goes to school in his father’s car. He likes watching TV in the evening.

①人的胃液里含有少量盐酸．

②可溶性钡盐会使人中毒．

试回答：透视检查胃病时，让患者口服硫酸钡是否会使人中毒？____

能否用碳酸钡代替硫酸钡？____原因是____．