ACT Math Practice Question

Let the function $f$ be defined as $f(x) = -9x^2$. In the standard $(x,y)$ coordinate plane, the graph of $y = f(x)$ undergoes a transformation such that the result is the graph of $y = f(x) - 4$. Under this transformation the graph of $y = f(x)$ is:

1. A.shifted downward 4 coordinate units.
2. B.shifted left 4 coordinate units.
3. C.stretched horizontally by a factor of 4.
4. D.stretched vertically by a factor of 4.