The best piece of evidence that the man and the girl are from two different countries is option B: The man is specifically described as "The American," whereas the nationality of the girl is unstated.
This evidence suggests that the man is from the United States, while the girl's nationality is not mentioned. Since the man is identified as American, it implies that he is from a different country than the girl.
This piece of evidence is clear and direct, as it directly states the nationality of the man while leaving the girl's nationality unknown. This implies that they are likely from two different countries.