If the directrix of a parabola is the horizontal line y = 3, what is true of the parabola?

For a vertical parabola with vertex at the origin, the equation is x² = 4py, its focus is (0, p), and its directrix is y = −p. Setting the directrix equal to y = 3 gives p = −3, so the focus is (0, −3) and the equation is x² = −12y. Therefore, choice B is correct.

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