To become a citizen of the united states you must

To become a U.S. citizen you must meet the following requirements:

You must be 18 years of age or older.

You must have authorization to live and work in the U.S. on a permanent basis (informally known as a green card) for at least five years (or three years, if married to a United States citizen).

Explanation:

the answer is option a.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.