ON HER TOES; After the lead ballerina Cristina drops out, the understudy Stacey Duncan (Tracey Ullman) goes through weeks of grueling training to star in the lead role in ""The Nutcracker."" TINA AND THE PROFESSOR; Tina goes out on a blind date with an ecentric and boring high school biology teacher (Dan Castellaneta). (She must be really getting desperate.) THE HIGH AND THE NOT SO MIGHTY; The USO troup Lisa Morgan and the Mob (Tracey Ullman, Sam McMurray and Joe Malone) are on a U.S. Army plane that is going down in the Pacific and they decide to sing one last song before they all bail out to their doom. GONE FISHIN; Bart and Homer go fishing on a river where they have problems with everything.