Final answer:
The length of AB on the graph cannot be determined without additional information.
Step-by-step explanation:
The approximate length of the line segment AB on the graph can be determined by measuring the distance between the two endpoints of the line. However, without the graph or any specific values, it is not possible to provide an exact answer. Therefore, the correct response would be that the length of AB cannot be determined without additional information. None of the options A) 2.5 units, B) 4 units, C) 6 units, or D) 8.5 units can be confidently selected without more context.