His credulous nature often landed him in trouble.

Answer: Option D

Dreamy : having a magical or pleasantly unreal quality; dreamlike.
Naughty : (especially of a child) badly behaved; disobedient.
Innocent : not guilty of a crime or offence.
Trusting : showing or tending to have a belief in a person's honesty or sincerity; not suspicious.
Credulous : having or showing too great a readiness to believe things.

Synonym of Credulous is Trusting