Question

A 24-month-old boy is brought to the clinic for a routine well-child visit. His parents have no specific concerns. On developmental assessment, the boy is able to run well, kick a ball, and walk up and down the stairs placing both feet on each step. He can build a tower of six cubes, turn the pages of a book one at a time, and remove his shoes. He has a vocabulary of approximately 50 words, uses two-word phrases, and his speech is understood by strangers about half of the time. When in the waiting room, he plays with his own toys alongside other children but does not directly interact with them. Physical examination is unremarkable. The pediatrician provides anticipatory guidance to the parents regarding the developmental milestones expected over the upcoming year. Which of the following skills is this patient most likely to acquire by his next annual visit at 36 months of age?