The correct option is A Publisher of that newspaper.
The word "defamation" is an all- encompassing term that covers any statement that hurts someone's reputation. If the statement is made in writing and published, the defamation is called "libel". If the statement , being hurtful, is spoken, the statement is "slander". In the above situation, the publisher of the newspaper published the defamatory article, hence he has committed libel.