Final answer:
The statement that justifies why angle EBC measures 90° is 'The sum of the measures of complementary angles is 90 degrees'. This implies that if angle EBC is one half of a complementary pair, its measure should indeed be 90 degrees.
Step-by-step explanation:
The statement that justifies why ∠EBC measures 90° is b. The sum of the measures of complementary angles is 90 degrees. This statement suggests that if ∠EBC is a part of a complementary pair of angles, then its measure should indeed be 90 degrees as complementary angles sum up to 90°. Options a, c, and d do not directly relate to the measurement of ∠EBC. A linear pair is a pair of adjacent, supplementary angles, but these add up to 180°, not 90°. Vertical angles are congruent but this fact doesn't guarantee a 90° measurement. Alternate interior angles are congruent in parallel lines cut by a transversal, but this is not related to a 90° angle measurement either.
Learn more about Complementary Angles