Until the 1960s, Why Were Actors in Almost Every Film

Until the 1960s, why were actors in almost every film, whether period or contemporary, required to wear wigs?

A) Hair styling was too costly.
B) It was feared that the audience would not recognize the star.
C) Wigs reflected light better than real hair.
D) An actor's real hair could be the source of a continuity error.
E) The star's contract prevented it.