Lily began a plan for this proof. Since ∠1 and ∠2 are supplementary and ∠1 and ∠3 are supplementary, then m∠1+m∠2=180° and m∠1+m∠3=180°. If she can get m∠2 and m∠3 to both equal the same expression, she can use the transitive property of equality to set them equal to each other.
How can Lily get m∠2 and m∠3 to both equal the same expression?

options:
A. She can measure m∠2 and m∠3 with a protractor.

B. She can subtract 180° from both sides of m∠1+m∠2=180° and m∠1+m∠3=180°.

C. She can subtract m∠1 from both sides of m∠1+m∠2=180° and m∠1+m∠3=180°.

D. She can subtract m∠1 from both sides of m∠1+m∠2=180°, and subtract m∠3 from both sides of m∠1+m∠3=180°.