Answer:
Line c ║ line d, applying the converse of the alternate exterior angles theorem.
Explanation:
See the given diagram attached.
It is given that ∠ 11 = ∠ 13.
Hence, from this we can conclude that line c ║ line d, applying the converse of the alternate exterior angles theorem.
The alternate exterior angle theorem says that if one line is the transverse line of any two other parallel lines then the alternate exterior angles so generated will be equal. (Answer)