Find fx(x,y) and fy(x,y), and explain why f(x,y) has no local extrema. f(x,y) = 4.4 -2.1x +7.2y + 0.4y3+x2 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 functions fx(x,y) and fy(x,y) are never equal to each other. O B. The function fy(x,y) is always positive while the function fx(x,y) is always negative. O C. The function fy(x,y) can never equal zero. O D. The function fx(x,y) can never equal zero