Concept:A firm gains cost advantages from the overall growth of the industry and its location, not from its own internal expansion.
Explanation:An industrial estate groups many small firms together in one area.
These firms share common facilities such as roads, electricity, water supply, and drainage.
They also benefit from pooled services like repair workshops, banking, research centers, and trained labor.
Sharing these facilities helps reduce each firm's average cost of production.
Such savings arise because the industry itself is growing and concentrating in one location.
These benefits do not depend on the size or internal management of the individual firm.
Hence, this cost advantage is called an external economy of scale.
Government protection, technological improvements, and financial gains are not guaranteed simply by locating in an estate.
Answer:D. external economies of scale