How Many Critical Points Does the Following Function Have $f ( x , y ) = 4 - \left( y ^ { 2 } + x ^ { 2 } \right)$

Multiple Choice

How many critical points does the following function have $f ( x , y ) = 4 - \left( y ^ { 2 } + x ^ { 2 } \right)$

A) four
B) one
C) two
D) three
E) none