A 3-year-old boy undergoes evaluation for autism spectrum disorder (ASD). The PMHNP conducting the examination utilizes a tool with four modules to aid in diagnosis. Which of the following is the PMHNP's tool?

Choice A reason: The M-CHAT is a screening tool designed to identify risk for ASD in toddlers, but it is not a diagnostic instrument with multiple modules. Choice B reason: Ages and Stages Questionnaires assess developmental milestones broadly and are not specific to autism diagnosis. Choice C reason: Children’s Behavior Checklist is a general behavioral assessment tool and does not provide module-based diagnostic evaluation for ASD. Choice D reason: The ADOS is a structured diagnostic tool with four modules tailored to age and language level, widely used for formal assessment and diagnosis of autism spectrum disorder.