已知命题 $P: \forall x \in(0,+\infty), 3 x \leq x^3$, 则 $\neg p$ 是
$\text{A.}$ $\exists x_0 \in(-\infty, 0], 3 x_0 \leq x_0^3$
$\text{B.}$ $\exists x_0 \in(0,+\infty), 3 x_0>x_0{ }^3$
$\text{C.}$ $\forall x \in(-\infty, 0], 3 x \leq x^3$
$\text{D.}$ $\forall x \in(0,+\infty), 3 x>x^3$