if 8=10 and 1=7, which describes all the lines that must be parallel?

Answer: Lines r and s and lines t and u must be parallel.
Step-by-step explanation:
If [tex]\angle{8}\cong\angle{10}[/tex] 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 [tex]\angle{1}\cong\angle{7}[/tex] 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.