Answer: A. Theory
Explanation: Before a scientist goes into research, he makes the best guess, which is a hypothesis to prove. Hypothesis are proved on a specific sample by conducting experiments and recording data and results from those experiments, which may or may not confirm the initial hypothesis, that is, the proof is correct or not. If the proof is correct, then this is the theory, that is, the collected data from the experiments conducted on the sample, and where the obtained data, ideas, concepts, complement each other, make this way the theory. So the theory obtained explains why an occurrence occurs according to a proven initial assumption.
Thus, Piaget also observed children's behaviour, that is, how children solve problems, collected data and proved the initial hypothesis, linking different concepts and behaviours into one theory.
