A 22- year- old woman is brought to the hospital after being found wandering on a school playground. She is not able to read or fill out basic paperwork. On exam, she is noted to be pursuing the picture books in the pediatric waiting area and laughing in a childlike manner. She is wearing a T-shirt, sweatpants, and shoes with hook-and-loop fasteners and has a wristband with her identification and her mother's contact information. The woman can say her name and address and answer simple yes/ no questions but cannot answer compound or complicated questions. She begins to cry after not being able to answer many questions. A review of her records indicates that she has not psychiatric hx but still sees her pediatrician, accompanied by her mother. Recent testing places her at an IQ of 50. She has no basic laboratory abnormalities and a negative urine toxicology screen. What is the likely diagnosis?

A. Conduct disorder.
B. Dissociative identity disorder.
C. Intellectual disability (intellectual developmental disorder).
D. Selective mutism.