By the end of the preoperational stage, children are able to understand the idea that actions, events, and outcomes are related to one another in fixed patterns, and this is called

Functionality

Explanation:

Functionalism refers to a psychological theory that takes into account mental life and actions in terms of active adaptation to the environment of the individual. By the end of the preoperational stage as prescribed by Piaget's theory of cognitive development, the child's development consists of building experiences about the world through adaptation and process is called functionalism.

i would say b. research typically uses a variety of sources

good question. i'll be looking into that. (this is a joke sir)