Underwriter is a person, who

Who arranges insurance policy
Manages import and export
Promises to purchase share unpurchased by public
Sells things on commission

The correct answer is: A. Who arranges insurance policy.

An underwriter is a person or organization that assumes the risk of loss for an insurance policy. They assess the risk and set the premium, and they are responsible for paying out claims if the insured event occurs.

Option B is incorrect because an importer or exporter is a person or organization that buys or sells goods from or to another country.

Option C is incorrect because an underwriter does not promise to purchase shares unpurchased by the public. This is the role of an investment bank.

Option D is incorrect because an underwriter does not sell things on commission. This is the role of a salesperson.