Concept:A chamber of commerce is a local association of business people in a town or area who unite to promote their common business interests.
Explanation:The question describes people who are engaged in trade and industry in a particular area coming together.
Such a coming together forms a local business network.
This network is known as a chamber of commerce.
A trade association is limited to a particular trade, not all traders and industrialists in an area.
An employers association represents only employers, and a trade union represents employees.
So the group in the question is best described as a chamber of commerce.
Answer:C. a chamber of commerce