To answer this question, let's analyze the statements made by Allan, Brian, Charlie, and yourself:

Allan said, "I guess it is not black." Brian said, "It is either brown or gray." Charlie said, "I know it is brown." You said, "At least one of you is right and at least one of you is wrong."

From these statements, we can deduce the following:

1. Allan's statement: Allan guesses that the horse is not black. This implies that the horse can be any color except black.

2. Brian's statement: Brian states that the horse is either brown or gray. This means that the horse cannot be black, as Allan already mentioned.

3. Charlie's statement: Charlie claims to know that the horse is brown. This statement contradicts Allan's statement, as Allan said the horse is not black. If the horse is brown, then Allan would be wrong.

4. Your statement: You state that at least one person is right and at least one person is wrong. Since Charlie claims to know the horse is brown, and Allan says it is not black, either Allan or Charlie must be wrong.

Based on the above information, we can conclude that the horse cannot be black or brown, as Allan's and Charlie's statements contradict each other. Therefore, the only remaining option is gray, as mentioned by Brian. Hence, the correct answer is option B) Gray.

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