Which of the following is an example of external economies? (a) The c

Which of the following is an example of external economies?

(a) The cost of per unit produced in manufacturing goods falls as the industry size grows.
(b) The cost of per unit produced falls as the firm size, not the industry size, grows.
(c) The cost of per unit produced in manufacturing goods increases as the industry grows.
(d) The cost of per unit produced falls as the size of the firm grows.

ANSWER

(a)