Concept:Piaget's theory of cognitive development describes distinct stages children go through as their thinking abilities evolve.Explanation:According to Jean Piaget's theory, the stage where children can test hypotheses, think multidimensionally, and engage in abstract thought is the Formal Operational Stage.This stage typically begins around age 11 and continues into adolescence.In this stage, children develop the ability to think logically about abstract concepts and hypothetical situations, moving beyond concrete experiences.They can consider multiple possibilities and perspectives, which is crucial for problem-solving involving hypothesis testing.The other stages are:- Sensory Motor Stage (0-2 years): Learning through senses and motor actions.- Pre-operational Stage (2-7 years): Development of language and symbolic thought, but thinking is egocentric and lacks logic.- Concrete Operational Stage (7-11 years): Development of logical thought about concrete events, understanding conservation and classification.Answer:C. Formal operational stage