Final answer:
Form I-9 is used to verify that an employee is a U.S. citizen as part of the employer's legal obligations under the Immigration Reform and Control Act of 1986. The correct option is c.
Step-by-step explanation:
The form used to verify that an employee is a U.S. citizen is Form I-9. This form was introduced following the passage of the Immigration Reform and Control Act of 1986, which prohibits the hiring of illegal immigrants and requires employers to verify and record the identity and employment authorization of each new employee.
Employers must complete Form I-9 for each new employee, which includes reviewing documents that establish the employee's identity and eligibility to work in the United States.
It's important to note that while Form W-2 and Form W-4 are related to taxes and withholding, and Form CMS-1500 is related to healthcare billing, they are not used to verify citizenship or work authorization. The correct option is c.