In order to circumscribe a circle on a triangle, which line must you construct? a. median b. altitude c. diagonal d. perpendicular bisector

The answer is the option d.Perpendicular bisector.

Explanation:
 
 By definition, a circumscribe circle passes through the three vertices of the triangle and to its constrution, you have to draw the triangle and then construct a perpendicular bisector to each side of it. The point where these perpendicular bisectors intersect each other, will be the center of the circle. Then, you should place the compass on the center point to draw the circle.