Find f (x,y) and fy(x,y), and explain why f(x,y) has no local extrema. f ( x , y ) = 3 x + 3y + 8 . . . . fx (x,y) = fy ( x,y ) = Choose the best explanation below for the reason that f(x,y) has no local extrema. O A. The second derivative test fails because AC - B2 = 0. O B. The functions fx(x,y) and fy(x,y) have no local extrema. C. The functions f(x,y) and fy(x,y) are non-zero for all (x,y). O D. The functions f(x,y) and fy(x,y) are never equal to each other