What American singer, film actor and comedian, suddenly stood up during a performance of Gershwin's Liza (All the Clouds'll Roll Away) and started singing?  
Liza (All the Clouds'll Roll Away): "Liza (All the Clouds'll Roll Away)" is a song composed by George Gershwin with lyrics by Ira Gershwin and Gus Kahn. Liza (All the Clouds'll Roll Away):  On the show's opening night in Boston on June 25, 1929, Keeler's husband and popular singer Al Jolson suddenly stood up from his seat in the third row and sang a chorus of the song, much to the surprise of the audience and Gershwin himself. Al Jolson: Al Jolson (born Asa Yoelson; May 26, 1886 – October 23, 1950) was an American singer, film actor, and comedian.
i don't know