Final answer:
The responsibility of first-line managers is subunit performance management. Therefore, the correct answer is a. Subunit performance management.
Step-by-step explanation:
A: Subunit performance management is one of the responsibilities of first-line managers. They are responsible for overseeing the performance of individual teams or subunits within an organization, ensuring that they meet their goals and objectives.
B: Teaching and training is typically the responsibility of middle-level managers or trainers who specialize in employee development and learning.
C: Change management is a higher-level strategic responsibility, usually handled by top-level managers who are responsible for steering the organization during periods of change or transformation.
D: Strategy implementation is also a higher-level responsibility that falls within the purview of top-level managers who formulate and execute strategic initiatives.
Therefore, the correct answer is a. Subunit performance management.