A. $f(x, y) = 2y^{5}-6x^{5}$
$\nabla f(x, y) =$
B. $f(x, y) = -6x^{5}y^{5}$
$\nabla f(x, y) =$
C. $f(x,y,z) = 2y^{5}-6x^{5}-7z^{4}$
$\nabla f(x,y,z) =$
D. $f(x,y,z) = -6x^{5}y^{5}z^{4}$
$\nabla f(x,y,z) =$
E. $f(x, y) = \cos^{5}\!\left(-6x\right)+\sin^{5}\!\left(2y\right)$
$\nabla f(x, y) =$