Answer:
d. a group of firms producing products that are close substitutes.
Step-by-step explanation:
An industry -
It refers to the sector of the society , which is responsible for the production of various goods and services within the boundaries of the society , is referred to as an industry.
The profit and success of the country's economy reflects the prosperity of the country .
Hence , from the given information of the question,
The correct option is d.