Line AB is parallel to EF. Transversal GJ crosses line AB at K and crosses line EF at L. The measure of angle ELJ is 120 degrees. Daniel is constructing a fence that consists of parallel sides line AB and line EF. Complete the proof to explain how he can show that m∠GKB = 120° by filling in the missing justifications.

Statement Justification

line AB ∥ line EF

m∠ELJ = 120° Given

m∠ELJ + m∠ELK = 180° Linear Pair Postulate

m∠BKL + m∠GKB = 180° Linear Pair Postulate

m∠ELJ + m∠ELK = m∠BKL + m∠GKB Transitive Property

∠ELK ≅ ∠BKL 1.

m∠ELK = m∠BKL 2.

m∠ELJ + m∠ELK = m∠ELK + m∠GKB Substitution Property

m∠ELJ = m∠GKB Subtraction Property

m∠GKB = m∠ELJ Symmetric Property

m∠GKB = 120° Substitution

Answer choices: 1. Alternate Interior Angles Theorem; 2. Definition of Congruence

1. Alternate Exterior Angles Theorem; 2. Substitution Prope