He is looking forward his father. A. of receiving B. of hearing from C. to hearing from D. to hear from 答案:C如图,点O是已知线段AB上一点,以OA为半径的⊙O交线段AB于点C,以线段OB为直径的圆与⊙O的一个交点为D,过点A作AB的垂线交BD的延长线于点M.(1)求证:BD是⊙O的切线;(2)若BC,BD的长度是关于x的方程x2-6x+8=0的两个根,求⊙O的半径;(3)在上述条件下,求线段MD的长.