" Theorem: A triangle has at most one obtuse angle. Francisco is proving the theorem above by contradiction. He began by assuming that in ∆ABC, ∠A and ∠B are both obtuse. Which theorem will Francisco use to reach a contradiction?
a. If two angles of a triangle are congruent, the sides opposite the angles are congruent.
b. If two supplementary angles are congruent, each angle measures 90°.
c. The largest angle in a triangle is opposite the longest side.
d. The sum of the measures of the angles of a triangle is 180°. 3"