Question

Amanda is writing a proof for the theorem stated below.

Theorem: The sum of interior angles of a triangle is 180°.

She first drew the figure shown below.
Which theorem will she most likely use in the proof?

Supplements of congruent angles are congruent.

If two angles of a triangle are congruent, the sides opposite these are congruent.

All straight angles are congruent.

Corresponding angles formed by parallel lines and their transversal are congruent.