Complex sentence: The studio would then screen test North for Monroe's roles, during which North wore Monroe's own studio wardrobe, in "The Girl in Pink Tights" and "There's No Business Like Show Business," as a threat to Monroe.
Split into simpler sentences: The studio would then screen test North for Monroe's roles. During the screen tests of "The Girl in Pink Tights" and "There's No Business Like Show Business," North wore Monroe's own studio wardrobe, as a threat to Monroe.