Refer to the diagram below for problems 18-20.

From each given statement, select the definition, property, postulate, or theorem that leads to the statement you are asked to prove.

18. (L23) Given: m n Prove: 1 7

A. Vertical angles are congruent.

B. If two parallel lines are cut by a transversal, then alternate interior angles are congruent.

C. If two parallel lines are cut by a transversal, then corresponding angles are congruent.

D. If two parallel lines are cut by a transversal, then interior angles on the same side of the transversal are supplementary.

E. If two angles form a linear pair, then they are supplementary.

19. (L27) Given: 2 and 7 are supplementary Prove: m n

A. Definition of parallel lines

B. If two lines form congruent alternate interior angles with a transversal, then the lines are parallel.

C. If two lines form congruent corresponding angles, then the lines are parallel.

D. If two lines form supplementary interior angles on the same side of a transversal, then the lines are parallel.

E. If two lines form congruent alternate exterior angles, then the lines are parallel.

20. (L17) Given: Lines m and t intersect Prove: 3 and 4 are supplementary

A. Definition of supplementary angles

B. Vertical angles are congruent.

C. If two parallel lines are cut by a transversal, then interior angles on the same side of the transversal are supplementary.

D. Definition of a linear pair E. If two angles form a linear pair, then they are supplementary.

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