Night after night

Young and attractive Berinice seduces her professor to get what she desires - a passionate encounter and a toe-curling climax. Initially, Zack didn't realize Berinice's intentions, believing she sought academic support. However, as desire kindled between them, giving Zack a prominent bulge. Despite attempts at instruction, they both gave in to primal urges, leaving Zack astonished by Berinice's carnal knowledge. Following her climax, Berinice offered Zack the choice of where to release his tension. Can you predict his selection?