Concept:An association of businesses in the same trade or industry that come together to protect and promote their common interests.
Explanation:Computer distributors are traders engaged in the same line of business.
When such traders form an association to safeguard and promote their interests, it is called a trade association.
A chamber of commerce brings together businesses from different trades, not only one trade.
A cooperative society is formed for mutual economic benefit, not specifically to protect trade interests.
A trade union is an association of workers or employees, not business owners or distributors.
Therefore, the association formed by computer distributors is best described as a trade association.
Answer:C. trade association