Conversation so far:
What was Judy Garland's role in The Wizard of Oz?
Dorothy Gale.
Did she sing any songs?
"Over the Rainbow".
What was The  Wizard of Oz based on ?
a film based on the 1900 children's book by L.
Frank Baum.

Question: How long did it take to complete the movie?
Self-contained rewrite: How long did The Wizard of Oz take to complete?