The act that granted a pardon to undocumented immigrants already living in the United States is the Immigration Reform and Control Act of 1986. This act provided amnesty to certain undocumented immigrants who had been living in the United States continuously since January 1, 1982. It allowed them to apply for legal status and eventually become lawful permanent residents.
The other options listed are:
1. McCarran-Walter Act of 1952: This act focused on immigration and nationality, but it did not grant a pardon to undocumented immigrants.
2. Refugee Act of 1980: This act revised U.S. immigration law regarding refugees, but it did not specifically address granting a pardon to undocumented immigrants already in the U.S.
3. Immigration Act of 1965: This act abolished the national origins quota system, but it did not grant a pardon to undocumented immigrants.
Therefore, the correct answer to the question is the Immigration Reform and Control Act of 1986.
