Final answer:
At six months, infants reach several developmental milestones, including improved vision, ability to pick up objects, and anxiety towards strangers.
Step-by-step explanation:
At six months of age, an infant reaches several milestones in their physical and cognitive development. They can pick up and transfer objects, pull themselves into a sitting position, and start to show anxiety towards strangers. Their vision improves, enabling them to notice colors and discriminate depth. They also begin vocalizing two-syllable sounds like "mama" or "dada."