Final answer:
Alprazolam option (C) is likely the medication a doctor would prescribe for Gary Lewis's anxiety during drives as it is an anxiolytic commonly used to treat anxiety disorders.
Step-by-step explanation:
The psychiatric medication a doctor might prescribe for Gary Lewis, who is moderately intellectually disabled and experiences anxiety during drives to the park, could be Alprazolam (option C). Alprazolam is an anxiolytic and part of a class of medications called benzodiazepines, which are commonly used to treat anxiety disorders. It works by enhancing the effects of a natural chemical in the body (GABA), which has a calming effect. Medications like Propranolol can be used for situational anxiety but it is primarily a beta-blocker used for heart conditions. Risperidone is an antipsychotic mainly used for treating schizophrenia and bipolar disorder, but sometimes prescribed for aggression and severe agitation in patients with intellectual disability. Morphine is an opioid analgesic and is not appropriate for treating anxiety due to its high potential for addiction and side effects unrelated to anxiety treatment.