Which of the following statements is not true?

an angle bisector can be a median of a triangle.
a perpendicular bisector can be an altitude of a triangle.
a median can be an altitude of a triangle.
all of the statements are true.

All of the statements has the qualifier "can be".
This means that we need just one single in each example to make the statement true.

In an equilateral triangle, medians, angle bisectors, altitudes and perpendicular bisectors are all coincident, which makes the first three statements true.  This in turn makes the fourth statement true.

So there are no false statements.

Bis the right answer