Correct Answer: Definitive

Solution : The second option is correct.

The underlined word in the sentence is suspicious, indicating a lack of trust or belief in someone or something. The most appropriate antonym from the options provided would be definitive, as it signifies something that is clear, certain, or conclusive.

The meanings of the other options are as follows:

• Ambiguous means unclear or has multiple interpretations.
• Doubtful means uncertain or hesitant.
• Queer means strange or odd.

Therefore, the correct answer is definitive.