Concept:An underwriter guarantees to buy unsold shares after a public offer.Explanation:In a public issue, the company wants to ensure the full amount is raised.An underwriter is a firm or person on the stock exchange that agrees to purchase any shares not bought by the public.This reduces the risk of the public offer failing.A broker buys and sells on behalf of clients, a stag applies for shares to sell for profit, and a jobber is a market maker who deals with brokers, not the public.Answer:D. An underwriter