PLEASE ANSWER Select the correct answer.
Caroline rewrote a quadratic equation in vertex form by completing the square, but her work has errors.

Identify the first error in her work.

A.
She incorrectly factored out the value of a.
B.
She subtracted the wrong value to maintain balance after completing the square.
C.
She incorrectly combined the constant terms.
D.
She squared the wrong value when completing the square.