Answer:
Option A: Because this is a rectangle, I would show that each vertex is made up with lines that have opposite reciprocal slopes.
Explanation:
A rectangle is a quadrilateral with four right angles.
Each right angle is made up of two perpendicular lines forming a vertex
And then proving this that all perpendicular lines have negative reciprocal slope.
It isn't always necessary to employ the idea of using a parallelogram first although it might be useful.