Final answer:
The sentence that indicates a setting of the United States in the 1920s is option B, utilizing 1920s American slang and reflecting the historical context of the film industry.
Step-by-step explanation:
The sentence that would indicate the setting is the United States in the 1920s is: B. The film critics felt that the new actor was the bee's knees, but the film itself was all wet. This sentence uses slang terms like 'the bee's knees' and 'all wet', which were popular during the 1920s in America, reflecting the unique cultural vernacular of the era.
The mention of film critics also hints at the growing film industry in Hollywood during the 1920s, which was a significant cultural development. Sentences A and D refer to periods related to World War II, which would indicate a setting of the 1940s or later. Sentence C, describing a gunslinger, could suggest an earlier time period such as the Wild West era.