Final answer:
AB is half the length of AD since B bisects AD, and with AD being 12, AB is therefore 6.
Step-by-step explanation:
The question given involves a line segment AD that is bisected by point B and further divided into two segments where point C is the midpoint of BD. Given that AD has a total length of 12, the goal is to find the length of segment AB.
Since B bisects AD, we know that AB is equal to BD. Moreover, because C is the midpoint of BD, AC and CD are of equal length. Since the total length of AD is 12, and AB equals BD, seeking the length of AB is essentially asking for half the length of AD. Thus,
AB = BD = AD/2 = 12/2 = 6.
The correct answer is A) 6.