Place one vertex v of the tetrahedron at the origin such that the opposite face, triangle pqr, is parallel to the xy-plane. consequently, the z-axis goes through the center c of the opposite face. make pq parallel to the x-axis and use cross sections parallel to the xy-plane. set up the integral that gives the volume of the solid. use increasing limits of integration. select the correct choice below and fill in the answer boxes to complete your choice.