y = –3x2 – 12Axis of symmetry:

The equation is y = −3x² − 12, with no x-term. For a quadratic y = ax² + bx + c, the axis of symmetry is x = −b/(2a); here b = 0, so x = 0. Therefore, the axis of symmetry is x = 0, choice D.

AI-written and checked against the verified answer.