If $f ( x , y ) = \frac { x y } { x ^ { 2 } + y ^ { 2 } }$

Multiple Choice

If $f ( x , y ) = \frac { x y } { x ^ { 2 } + y ^ { 2 } }$ then $\lim _ { ( x , y ) \rightarrow ( 0,0 ) } f ( x , y )$

A) exists
B) does not exist
C) is equal to 0

D) is equal to $\frac { 1 } { 2 }$
E) is equal to 1