<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 4-year-old boy is brought to a pediatrician by his parents for a consultation after his teacher complained about his inability to focus or make friends at school. They mention that the boy does not interact well with others at home, school, or daycare. On physical examination, his vital signs are stable with normal weight, height, and head circumference for his age and sex. His general examination and neurologic examination are completely normal. A recent audiological evaluation shows normal hearing, and intellectual disability has been ruled out by a clinical psychologist. Which of the following investigations is indicated as part of his diagnostic evaluation at present?? A: Magnetic resonance imaging MRI of brain, B: Positron Emission Tomography PET scanning of head, C: Electroencephalography, D: Genetic testing for methyl-CpG-binding protein 2 MECP-2 gene mutations, E: No further testing is needed,  <response>: This is a clinical vignette describing a 4-year-old boy with difficulties in social interaction and focusattention. The key findings are inability to interact well with others at home, school, or daycare, and inability to focus or make friends at school. Physical exam, hearing, and intelligence are normal. This presentation is most consistent with autism spectrum disorder. The question asks about the next best diagnostic test to perform. MRI brain would look for structural abnormalities in the brain which are not typically seen in autism. PET scanning is not routinely indicated. EEG may be considered in some cases but is also not a first-line test. Genetic testing can be done but is not the next best test in this scenario. The diagnosis of autism spectrum disorder is primarily clinical, so no further testing is needed at this time.E: No further testing is needed 