Step 1: Understand employee development.
Employee development involves improving the skills and abilities of employees through various activities such as training, promotions, and transfers.
Step 2: Evaluate the options.
- Development includes all aspects: promotion, transfer, and training. These elements help employees grow within the organization, advancing in their careers and learning new skills.
Step 3: Conclude.
The correct answer is All of these, as they all contribute to the overall development of employees.
Final Answer:
\[
\boxed{\text{All of these}}
\]