Question: "Which number Symphony of Beethoven's is often used commercially?"  Context: "Certain staples of classical music are often used commercially (either in advertising or in movie soundtracks). In television commercials, several passages have become clichéd, particularly the opening of Richard Strauss' Also sprach Zarathustra (made famous in the film 2001: A Space Odyssey) and the opening section "O Fortuna" of Carl Orff's Carmina Burana, often used in the horror genre; other examples include the Dies Irae from the Verdi Requiem, Edvard Grieg's In the Hall of the Mountain King from Peer Gynt, the opening bars of Beethoven's Symphony No. 5, Wagner's Ride of the Valkyries from Die Walküre, Rimsky-Korsakov's Flight of the Bumblebee, and excerpts of Aaron Copland's Rodeo."  Answer:
5