Concept:Pressure groups combine individual demands into unified common goals.Explanation:Pressure groups receive varied concerns from different individuals.They cannot present each concern separately to the government.Instead, they merge and harmonize these concerns into a single collective position.This process is called interest aggregation.It helps the group speak with one voice and increases its influence.Other options like articulation or mobilisation refer to expressing or activating support, not merging concerns.Answer:D. interest aggregation.