Step 1: Recall sector classification.
- Primary = extraction (agriculture, mining).
- Secondary = transformation of raw materials into finished goods → industries.
- Tertiary = services.
Step 2: Apply to the question.
The secondary sector = industrial sector, since it converts raw resources into usable products (factories, electricity, manufacturing).
Step 3: Eliminate.
(A) Agriculture = primary.
(C) Service = tertiary.
(D) All of these = wrong, only one is correct.
Step 4: Conclusion.
Correct answer: (B) Industrial sector.