In verifying the identities and credentials of job applicants, employers must use the revised form I$-9$ for each employee hired and must $\_\_\_\_\_.$

a$.$ send copies of all documents submitted by employees to the Immigration and Naturalization Service within $48$ hours of hiring

b$.$ contact the Department of Homeland Security within $24$ hours if a registered alien or an illegal alien applies for a job in the transportation sector

c$.$ permit annual compliance audits of HR records by U$.$S$.$ Immigration and Customs Enforcement agents

d$.$ determine within $72$ hours of hiring whether a job applicant is a U$.$S$.$ citizen, registered alien, or illegal alien