Find the Derivative of the Function $f ( x ) = \sqrt { x - 4 }$

Multiple Choice

Find the derivative of the function. $f ( x ) = \sqrt { x - 4 }$

A) $\frac { 12 } { x ^ { 4 } }$
B) $\frac { 1 } { 2 \sqrt { x + 4 } }$
C) $2 x + 4$
D) $\frac { 1 } { 2 \sqrt { x - 4 } }$
E) $- \frac { 1 } { 2 \sqrt { x + 4 } }$