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

To find the correct one-word substitute for the phrase "The original inhabitants of a country", let us analyze the meaning of each of the given options:

1. Primitive: Relating to, denoting, or preserving the character of an early stage in the evolutionary or historical development of something. It does not specifically denote the inhabitants of a country.
2. Citizens: Legally recognized subjects or nationals of a state or commonwealth, either native or naturalized. Citizens do not necessarily have to be the original inhabitants of that country.
3. Aborigines: The people who have existed in a country or region from the earliest times or from before the arrival of colonists. This directly matches the definition of "the original inhabitants of a country."
4. Aliens: Belonging to a foreign country or nation. These are not native or original inhabitants.

Therefore, the most appropriate one-word substitute is Aborigines.