Concept:Cognitive development is about how children think, learn, and understand the world. It improves when children actively explore and interact with a stimulating environment.Explanation:Piaget’s theory shows that children build knowledge by encountering new ideas and challenges. They learn best when their surroundings offer varied experiences. A rich environment with diverse materials and opportunities lets children discover, question, and adjust their understanding. Frequent testing or focusing only on individual work does not support this natural process. Collaboration and traditional methods can help, but the key is a rich and varied environment that encourages exploration.Answer:C. providing a rich and varied environment