Find the measure of ∠1. justify your answer.

a.
m∠1 = 60 because corresponding angles of parallel lines are supplementary.

b.
m∠1 = 120 because corresponding angles of parallel lines are congruent.

c.
m∠1 = 120 because same-side interior angles of parallel lines are congruent.

d.
m∠1 = 60 because same-side interior angles of parallel lines are supplementary.

The correct answer option is: B.  m∠1 = 120 because corresponding angles of parallel lines are congruent.

Step-by-step explanation:

We are given a diagram where two parallel lines are intersected by a transversal.

We know that, if two parallel lines are cut by a transversal, then the alternate interior angles formed are congruent.

So here, the angle numbered 1 and the angle measuring 120° are congruent.

Therefore, m∠1 = 120° so option B is correct.