Infant Development Question

A healthy seven‑month‑old boy presents with his parents for a well‑child visit. He was born at 39.5 weeks gestation via spontaneous vaginal delivery. After a pregnancy without complication, he and his mother went home after 24 hours. He is primarily breastfed with a small amount of solids and continues to be at the 50th percentile weight and 40th percentile length. The parents voice no concerns. Which of the following is the most appropriate developmental milestone for this child's age?...