Find f, (x,y) and f, (x.y), and explain why f(x,y) has no local extrema fix,y) = 4.6 - 1.3x +7.8y + 0.3y +x4 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 function f (x,y) can never equal zero. O B. The function f (x,y) is always positive while the function f (x,y) is always negative. O C. The function f, (x,y) can never equal zero O D. The functions fx (x,y) and fy(x,y) are never equal to each other