Final answer:
The Form I-9 is used to verify an individual's identity and authorization to work in the U.S., as required by the Immigration Reform and Control Act of 1986. It is unrelated to healthcare or government benefits.
Step-by-step explanation:
The Form I-9 is completed to verify the identity and employment authorization of individuals hired for employment in the United States. The correct answer to why it is necessary to complete the Form I-9 is C. It is a form that proves your identity to your employers. This process stems from the Immigration Reform and Control Act of 1986, which aims to prevent the hiring of undocumented immigrants by requiring employers to verify each employee's eligibility to work in the U.S. The I-9 form is not related to providing documentation to schools, receiving free health care, or establishing eligibility for government benefits. Instead, it has a specific function related to employment verification.