Question:  I'll Take Romance starred Grace Moore, Melvyn Douglas, Helen Westley, Stuart Erwin and this American film character best known for her portrayal of who?

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So This Is Love (film): So This Is Love (Also Known as "The Grace Moore Story" is a 1953 film directed by Gordon Douglas, based on the life of singer Grace Moore.  The film stars Kathryn Grayson as Moore, and Merv Griffin.  The story chronicles Moore's rise to stardom from 1918 to February 7, 1928 when she made her premiere at the Metropolitan Opera.

Chained (1934 film): Chained is a 1934 American film directed by Clarence Brown, starring Joan Crawford and Clark Gable, with supporting performances by Otto Kruger and Stuart Erwin.  The screenplay was written by John Lee Mahin, Albert Hackett and Frances Goodrich, based upon a story by Edgar Selwyn.

I'll Take Romance (film): I'll Take Romance is a 1937 romantic musical film directed by Edward H. Griffith, starring Grace Moore, Melvyn Douglas, Helen Westley, Stuart Erwin and Margaret Hamilton.

Passport Husband: Passport Husband is a 1938 American comedy film directed by James Tinling and written by Karen DeWolf and Robert Chapin.  The film stars Stuart Erwin, Pauline Moore, Douglas Fowley, Joan Woodbury, Robert Lowery and Harold Huber.  The film was released on July 15, 1938, by 20th Century Fox.

Sweetie (1929 film): Sweetie is a 1929 American musical film directed by Frank Tuttle and written by George Marion Jr. and Lloyd Corrigan.  The film stars Nancy Carroll, Helen Kane, Stanley Smith, Jack Oakie, William Austin, Stuart Erwin and Wallace MacDonald.  The film was released on November 2, 1929, by Paramount Pictures.

Ninotchka: Ninotchka is a 1939 American film made for Metro-Goldwyn-Mayer by producer and director Ernst Lubitsch which stars Greta Garbo and Melvyn Douglas.  It is written by Billy Wilder, Charles Brackett, and Walter Reisch, based on a screen story by Melchior Lengyel.  "Ninotchka" is Greta Garbo's first full comedy, and her penultimate film.  It is one of the first American movies which, under the cover of a satirical, light romance, depicted the Soviet Union under Joseph Stalin as being rigid and gray, in this instance comparing it with the free and sunny Parisian society of pre-war years.

Clothes (1920 film): Clothes is a 1920 American silent drama film produced and distributed by the Metro Pictures company.  It is based on a 1906 Broadway play, "Clothes", by Channing Pollock and Avery Hopwood.  The play starred Grace George with a young supporting player named Douglas Fairbanks.  A 1914 silent film was produced and is now lost.  This 1920 version from Metro starred Olive Tell.  By all accounts this version is lost as well.

Margaret Hamilton (actress): Margaret Brainard Hamilton (December 9, 1902 – May 16, 1985) was an American film character actress best known for her portrayal of the Wicked Witch of the West in Metro-Goldwyn-Mayer's classic film "The Wizard of Oz" (1939).

It Could Happen to You (1939 film): It Could Happen to You is a 1939 American comedy film directed by Alfred L. Werker and written by Lou Breslow and Allen Rivkin.  The film stars Stuart Erwin, Gloria Stuart, Raymond Walburn, Douglas Fowley, June Gale and Clarence Kolb.  The film was released on June 8, 1939, by 20th Century Fox.

Sunny (1941 film): Sunny is a 1941 film American film directed by Herbert Wilcox.  It was adapted by Sig Herzig from the Jerome Kern-Oscar Hammerstein II musical play "Sunny".  It stars Anna Neagle, Ray Bolger, John Carroll, Edward Everett Horton, Grace Hartman, Paul Hartman, Frieda Inescort, and Helen Westley.

Supporting paragraphs: I'll Take Romance (film) Margaret Hamilton (actress)
Answer: Wicked Witch of the West