Final answer:
During the storming stage of group development, the team leader should most encourage the voicing of disagreements. This is essential for resolving conflicts and building team cohesion as the group progresses through its development stages.
Step-by-step explanation:
The most important factor for a team leader to encourage during the storming stage of group development is C. Voicing of disagreements. At this stage, it is crucial for members to express their different opinions and concerns openly. This can lead to conflicts, which are a natural part of the team development process and necessary for the growth of the team. Ensuring these disagreements are voiced allows the team to address underlying issues, fostering a deeper understanding among members, and setting the stage for problem solving and consensus building. The storming phase is characterized by competition and conflict in personal relationships and can be a challenging stage to navigate without effective leadership.