Find All the Saddle Points of the Function $f ( x , y ) = x \sin \frac { y } { 2 }$

Multiple Choice

Find all the saddle points of the function. $f ( x , y ) = x \sin \frac { y } { 2 }$

A) $( 3 \pi n , 0 )$
B) $\left( 0 , \frac { \pi n } { 2 } \right)$
C) $( 2 \pi n , 1 )$
D) $$( 0,2 \pi n )$$
E) $\left( \frac { 2 n } { \pi } , 0 \right)$