Lecture 10 (Geometry) Right Angles, Angle Inequalities, and Exterior Angles

According to the course's convention, what does it mean for an angle to be a right angle?

1. A.Its measure is exactly ninety degrees.
2. B.Its two sides are perpendicular by definition.
3. C.It is an angle that is congruent to its own supplement.
4. D.It is half of a straight angle as measured in radians.