Given: Lines a and b are parallel and line c is a transversal.
Prove: ∠2 is supplementary to ∠8


What is the missing reason in the proof?

Statement Reason
1. a || b, is a transv 1. given
2. ∠6 ≅ ∠2 2. ?
3. m∠6 = m∠2 3. def. of congruent
4. ∠6 is supp. to ∠8 4. def. of linear pair
5. ∠2 is supp. to ∠8 5. congruent supplements theorem

A: vertical angles theorem

B: alternate interior angles theorem

C: corresponding angles theorem

D: alternate exterior angles theorem