According to paragraph 4, which of the following is true about the technical problems of early sound films? A. Linking images with recorded sound was a larger obstacle than weak sound amplification or fragile sound recordings. B. Sound films in the 1920s were unable to solve the technical flaws found in sound films before the First World War. C. Technical inadequacies occurred less frequently in early sound films than critics suggested. D. Critics assumed that it would be impossible to overcome the technical difficulties experienced with earlier sound films.