Select the option that can be used as a one-word substitute for the given group of words.

A person who regards the whole world as his country

Cosmopolitan

The word that can be used as a one-word substitute for "a person who regards the whole world as his country" is cosmopolitan.

• Convalescent means recovering from an illness or injury.
• Countryman means a person who lives in the same country as another person.
• Metropolitan means relating to or denoting a metropolis or large city.
• Cosmopolitan means familiar with and at ease in many different countries and cultures.

Cosmopolitan is the most appropriate word for the given group of words because it specifically refers to someone who regards the whole world as their country. It is derived from the Greek word kosmopolitēs, meaning "citizen of the world."