In which period did the studio system characterize Hollywood films?
O A. 1920s-1930s
OB. 1950s-1960s
OC. 1960s-1970s
OD. 1930s-1940s
O A. 1920s-1930s
OB. 1950s-1960s
OC. 1960s-1970s
OD. 1930s-1940s