Final answer:
First-level managers are those who supervise non-managerial employees and are directly responsible for the production of company products or services. The correct answer is option: a) First-level managers.
Step-by-step explanation:
Managers who train and supervise the performance of non-managerial employees, and who are directly responsible for producing the company's products or services, are categorized as first-level managers. These managers are on the frontline of the business operations, often interacting directly with the employees and ensuring that day-to-day activities align with the broader goals of the organization. They play a crucial role in implementing the plans devised by higher levels of management and are integral to the success of a company's productivity.