Answer: Lines r and s and lines t and u must be parallel.
Step-by-step explanation:
If which are alternate interior angle corresponding to line t and u.
then by Alternate interior angle property :
Lines t and u must be parallel.
If which are alternate exterior angle corresponding to line r and us.
then by Alternate exterior angle property :
Lines r and s must be parallel.
Hence, Lines r and s and lines t and u must be parallel.