Step 1: Understanding the Question:
The question tests a core concept from the Nature/Principles of Management syllabus.
Step 2: Identifying the correct option:
Recruitment (searching for and attracting a pool of candidates) has two broad sources — internal (promotion, transfer) and external (advertisement, employment exchanges, campus placement). Selection is a separate, later HR step of choosing the right candidate FROM the recruited pool — it is not itself a source.
Step 3: Why (A) Internal source is incorrect:
Internal source is a recognised category of recruitment.
Step 3: Why (B) External source is incorrect:
External source is a recognised category of recruitment.
Step 3: Why (D) Promotion is incorrect:
Promotion is a specific internal source of recruitment.
Final Answer:
Selection