Angelina wants to prove that vertical angles are congruent. She uses the diagram below to formulate her proof. Angelina has one step wrong in her proof. The steps of her proof are shown below. Mark the step that is INCORRECT.

A.
Linear pairs of angles are complementary, hence, m∠2 + m∠3 = 90°.

B.
Subtracting m∠3 from both sides of the above equation gives m∠2 = m∠4.

C.
In my proof, I used m∠2 + m∠3 = m∠3 + m∠4 to justify linear pairs.

D.
By definition of congruent angles, ∠2 ≅ ∠4. This will show that ∠2 and ∠4 are veritcal angles.