Question

if ∠8≅∠10 and ∠1≅∠7, which describes all the lines that must be parallel? only lines r and s must be parallel. only lines t and u must be parallel. lines r and s and lines t and u must be parallel. neither lines r and s nor lines t and u must be parallel.

Explanation:

Step1: Analyze ∠8 and ∠10

∠8 and ∠10 are alternate - interior angles. If ∠8≅∠10, then lines t and u are parallel by the alternate - interior angles converse.

Step2: Analyze ∠1 and ∠7

∠1 and ∠7 are corresponding angles. If ∠1≅∠7, then lines r and s are parallel by the corresponding angles converse.

Answer:

Lines r and s and lines t and u must be parallel.