Find a downward-pointing unit normal vector n to the surface r(0,0) = (p cos 0,2p sin 0,p) at the point (1, 2, 72). Select one: O a. }(0, 1, 272) Ob (2,1,–202) O co 1.0.623 Od 1.–2,-v2) 0.112.4-v>