The 1985 film "Return to Oz" is loosely based on which of L. Frank Baum's books?
Return to Oz:  It is loosely based on L. Frank Baum's "Oz" novels, mainly "The Marvelous Land of Oz" (1904) and "Ozma of Oz" (1907), yet is set six months after the events of the first novel, "The Wonderful Wizard of Oz" (1900) took place. The Marvelous Land of Oz:  Plot elements from "The Marvelous Land of Oz" are included in the 1985 Disney feature film "Return to Oz".
The Marvelous Land of Oz