Answer: Henry Cowell, Aaron Copland, Leonard Bernstein and John Cage.
Explanation:
Aaron Copland was a composer (and oscar winner) born in Slepy Hollow, New York.
Leonard Bernstein was a composer born in Lawrence, Massachusetts.
John Cage was a composer born in Los Angeles, California
and Henry Cowel was a composer born in Menlo Park, California.
So all of them are American composers. while some are more famous for their work in movies, like Copland, others are more famous for their work in musicals, like Bernstein. Maybe this question was oriented to "movie composers" or "opera composers", but as it is worded, all of them are right answers.
