Final answer:
Petra is a middle manager because her role includes implementing strategies from top management and coordinating with first-line managers to ensure these strategies are executed at the operational level.
Step-by-step explanation:
Petra, a plant manager, received an e-mail from the CEO directing a new focus on customer service and the need for plant managers to implement this policy with their lowest-level managers. In the context of organizational hierarchy, Petra would be classified as a D) middle manager. Middle managers are responsible for implementing the strategic directions set by top management and facilitating these strategies down to the first-line managers, who in turn ensure that front-line employees adhere to these strategic goals. In this scenario, Petra acts as the link between the top management and the first-line managers, and her role in coordination is a key characteristic of a middle manager.