Select from the drop-down menus to correctly complete the statements. By the triangle sum property, m∠2 + m∠3 + m∠4 = 180∘ . The sum of the measures of angles is 180° because they . Using the substitution property, m∠2 + m∠3 + m∠4 = m∠1 + m∠3 . Then, by the subtraction property of equality, m∠2 + m∠4 =