Reduce rational expressions to lowest terms: Error analysis

Raiden tried to reduce the following expression to lowest terms:

\frac{4 x^{2} - 12 x}{3 x^{2} + 15 x}

This is his work:

Factoring the numerator: $4 x^{2} - 12 x = 4 x (x - 3)$ ‍

Factoring the denominator: $3 x^{2} + 15 x = 3 x (x + 5)$ ‍

Reducing to lowest terms:

$\begin{aligned} \frac{4 x^{2} - 12 x}{3 x^{2} + 15 x} & = \frac{4 x (x - 3)}{3 x (x + 5)} \\ = \frac{4 (x - 3)}{3 (x + 5)} \end{aligned}$ ‍

Finding excluded values: $x \neq - 5$ ‍

What mistake did Raiden make?

(Choice A)
He didn't exclude $x = 3$ ‍, which makes the numerator equal to zero.
(Choice B)
He didn't exclude $x = 0$ ‍, which makes the denominator in the original expression equal to zero.
(Choice C)
He excluded $x = - 5$ ‍, which doesn't make the numerator equal to zero.
(Choice D)
He didn't factor the numerator correctly.

Precalculus