Final answer:
The correct statement is that AB equals BC because B is the midpoint of segment AC, which means AB and BC are congruent.
Step-by-step explanation:
If B is the midpoint of segment AC, then by definition, the segment is divided into two equal parts at point B. Therefore, the length of segment AB is equal to the length of segment BC. Without additional information about point D or the context in which it is mentioned, we cannot confirm the relationship between DB and other segments. Thus, the correct answer to the student's question is:
A. AB=BC
Segments AB and BC are equal in length because B is the midpoint of AC, hence they are congruent segments.