This episode's headline: World AIDS Day; Final Question; Angola's Agony; Strange Alliances. The guests include DR. TIMOTHY QUILL, University of Rochester; DR. CARLOS GOMEZ, University of Virginia; DR. ERIC CASSELL, Cornell Medical Center; ANDREW NATSIOS, World Vision; SHARON PAULING, Bread for the World; HERMAN COHEN, Former State Department Official; CORRESPONDENTS: MARGARET WARNER; LINDSAY TAYLOR; CLARENCE PAGE. Byline: In New York: ROBERT MacNeil; In Washington: JAMES LEHRER