Final answer:
A team leader seeking to leverage participatory planning should use a Group decision-making method, aligning with democratic leadership that encourages consensus building.
Step-by-step explanation:
If a team leader wants to tap the advantages of participatory planning, the type of decision-making method he or she should use is c) Group decision-making. This approach aligns with a democratic leadership style, facilitating group participation in all decision-making processes and aiming to build consensus before action is taken. It contrasts with authoritarian leadership, where communication and decisions flow from the top down and laissez-faire leadership, which is more hands-off. Participatory planning implies collective decision-making, which can reduce conformity costs, which are associated with the consolidation of decisions in the hands of a few, but may increase transaction costs associated with the time and effort needed to reach a consensus.