Question

the segment in this diagram that divides $overline{ab}$ into two congruent parts is called a(n): perpendicular bisector. angle bisector. parallel line

Explanation:

A perpendicular bisector divides a line - segment into two congruent parts and is perpendicular to it. The diagram shows a line perpendicular to $\overline{AB}$ and bisecting it.

Answer:

perpendicular bisector.