Answer:
Given,
p and r are parallel lines,
We have to prove that : ∠1 is supplementary to ∠7.
Thus, the column prove would be,
         Statement                                             Reason
1. Line p is parallel to line r.                 1. Given
2. ∠2≅∠7                                             2. Exterior alternate angle theorem,
3. m∠2=m∠7                                        3. Property of congruence,
4. ∠1 and ∠2 form a linear pair.          4. Adjacent angle on straight line,
5. ∠1 is supplementary to ∠2             5. Linear pair postulate
6. m∠1+m∠2=180°                                6. Supplementary angle property
7. m∠1+m∠7=180°                                 7. Substitution property
8. ∠1 is supplementary to ∠7               8. Supplementary angle property