Let $f ( x , y , z ) = \sqrt { x ^ { 2 } + y ^ { 2 } + z ^ { 2 } }$

Multiple Choice

Let $f ( x , y , z ) = \sqrt { x ^ { 2 } + y ^ { 2 } + z ^ { 2 } }$ . Then the maximum value of the directional derivative $D _ { \mathrm { u } } f ( 3,4,0 )$ is

A) 5
B) 3
C) 2
D) 1
E) $\frac { 1 } { 3 }$