Correct Answer:
C. have seen
The word "already" indicates that an action has been completed at some unspecified time before now, and its result is relevant to the present. This is a classic use case for the present perfect tense ("have seen"). The present perfect connects a past action to the present. "See" (simple present) is incorrect. "Saw" (simple past) would be used if a specific past time were mentioned (e.g., "I saw the movie yesterday"). "Had seen" (past perfect) would be used if there was another past event that this action preceded (e.g., "I had seen the movie before you mentioned it").