TOEFL Listening: TPO-TOEFL听力TPO - _0K0RCGMDCDY9X17R$

According to the professor, what was characteristic of sound films in the 1920s? A. Dialogues between characters were kept to a minimum. B. Many films were closely based on theater plays. C. Musical sound tracks were added to most films. D. Sounds were recorded separately and added to films later.