Which of the following statements is not true? a. an angle bisector can be a median of a triangle. b. a perpendicular bisector can be an altitude of a triangle. c. a median can be an altitude of a triangle. d. all of the statements are true.

The answer is choice D:

consider an isosceles triangle, all of these statements would hold true:

Note: The median of an isosceles triangle is always a perpendicular bisector of the opposite side. As such, it would also serve as the altitude of the triangle.