First-line managers are primarily responsible for:

First-line managers play a crucial role in the organizational structure by directly overseeing the daily operations and activities of employees who are involved in the production of goods and services. Their primary responsibility is to ensure that tasks are performed efficiently, effectively, and in alignment with the organization's goals. This includes managing individual team members, providing guidance, addressing any immediate issues that arise, and ensuring that both productivity and quality standards are met.

By focusing on daily activities, first-line managers enable frontline workers to stay on track with operational tasks and help facilitate communication between management and employees. This hands-on involvement is essential for maintaining day-to-day operations and ensuring that the team's contributions align with broader organizational objectives.

The other options, while related to managerial responsibilities, do not accurately reflect the primary duties of first-line managers. Directing middle managers pertains more to a different management level, making decisions that affect the entire organization relates to top management, and setting strategic vision is a task primarily handled by upper management. Thus, the focus of first-line managers is distinctly centered around the immediate operational level.