The question pertains to identifying a communication theory based on its description. Let's analyze the given options to comprehend which theory aligns with the described characteristics effectively:

• Agenda Setting by Maxwell McCombs and Donald L. Shaw: This theory suggests that media doesn't tell us what to think but rather what to think about. It focuses on the media's role in shaping public attention and prioritizing issues. This is not related to subtle effects and absorption as mentioned in the question.
• The Cultivation Theory by George Gerbner: This theory posits that prolonged exposure to media, particularly television, subtly influences and shapes the audience's perception of reality. Over time, individuals tend to adopt the symbolic meanings and images portrayed, which aligns perfectly with the description stating that mass media has subtle effects leading audiences to absorb dominant symbols, images, and messages unknowingly.
• Uses and Gratification Theory by Katz: This theory focuses on how individuals actively seek out media to satisfy specific needs and desires, emphasizing audience activity and purpose, which again differs vastly from the passive absorption described in the question.
• Soviet Communist Theory by Wilbur Schramm: This theory is about media functioning as a tool for the state to promote socialist ideologies, emphasizing control rather than subtle influence as described in the question.

Based on the explanation above, the correct answer is The Cultivation Theory by George Gerbner, as it specifically deals with the subtle and unconscious absorption of media messages by audiences, reflecting prolonged exposure effects.