Concept:Piaget's theory uses assimilation (fitting new ideas into existing mental structures) and accommodation (changing mental structures when new ideas don't fit).Explanation:Learning a linear equation and its solving techniques uses existing knowledge. So this is assimilation.Extending the same concept to a pair of linear equations may require changing the mental framework. This could raise the need for accommodation.Thus, option A correctly describes this sequence: introduction of linear equation as assimilation, and extending to pair as possible accommodation.Answer:Option A