The Set of Points On $4 x ^ { 2 } + y ^ { 2 } + 2 z ^ { 2 } = 50$

Multiple Choice

The set of points on $4 x ^ { 2 } + y ^ { 2 } + 2 z ^ { 2 } = 50$ at which the tangent plane is parallel to the xy-plane is

A) $\{ ( 0,0 , - 5 ) , ( 0,0,5 ) \}$
B) $\{ ( 0,0,5 ) \}$
C) $\{ ( 0,0 , - 5 ) \}$
D) $\{ ( 0,0 , - 3 ) \}$
E) $\{ ( 0,0,3 ) \}$