The curl of the gradient of the scaler field defined by $V=2x^2y+3y^2z+4z^2x$ is

- $4xy \textbf{a}_x+6yz \textbf{a}_y+8zx \textbf{a}_z$
- $4 \textbf{a}_x+6\textbf{a}_y+8 \textbf{a}_z$
- $(4xy+4z^2) \textbf{a}_x+(2x^2+6yz) \textbf{a}_y+(3y^2+8zx) \textbf{a}_z$
- $0$