Concept:The word "dubious" describes an attitude that is suspicious, doubtful, or not honest.Explanation:In the sentence, "dubious attitude" means his behaviour is questionable and makes people feel he cannot be trusted.This kind of dishonesty causes his friends to turn away from him.Among the options, "deceitful" best matches this meaning because it means dishonest or misleading.The other choices do not fit the sense of the sentence.Answer:A. deceitful