With the Cobb-Douglas Utility Function $U ( x , y ) = \sqrt { x y }$

With the Cobb-Douglas utility function $U ( x , y ) = \sqrt { x y }$ ,x and y are

A) net and gross substitutes.
B) net substitutes and gross complements.
C) net substitutes and neither gross substitutes or complements.
D) net and gross complements.