Find the Directional Derivative to the Given Function at the Specified

Multiple Choice

Find the directional derivative to the given function at the specified point $P$ in the direction of the vector $\vec { u }$ $f ( x , y , z ) = 2 z \sqrt { x y } , P = ( 2,2,3 ) , \vec { u } = \langle 1,1,1 \rangle$

A) $10$
B) $10 \sqrt { 3 }$
C) $\frac { 10 } { 3 }$
D) $\frac { 10 } { \sqrt { 3 } }$