Concept:The word “defend” means to guard or keep someone safe from harm.Explanation:In the given sentence, “defend his master” means to protect his master from danger.Among the options, “fortify” means to strengthen a place, “secure” means to make safe or fasten, “protect” means to shield from harm, and “cover” means to hide or place something over.The closest in meaning to “defend” is “protect”.Answer:C. protect