Let f x y 144 x A Describe the cross sections of the surface z f x y produced by cutting it with the planes y 1 y 4 and y 7 B Describe the cross sections of the surface in the planes x 1 x 4 and x 7 C Describe the surface z f x y y 2 A Choose the best description of the cross sections in the planes y 1 y 4 and y 7 OA Upper semicircles whose centers lie on the y axis OB Up opening parabola in the xz plane OC Down opening parabola in the yz plane D Lower semicircles whose centers lie on the x axis