Choice "D" is correct. An employee who has had social security tax withheld in an amount greater than the maximum for a particular year, may claim the excess as a credit against income tax, if that excess resulted from correct withholding by two or more employers.
Choice "a" is incorrect. The excess resulting from the correct withholding by two or more employers may only be claimed as a credit against income tax.
Choice "b" is incorrect. The employee may not seek reimbursement of the excess if the excess resulted from correct withholding by two or more employers.
Choice "c" is incorrect. The employee may not claim the excess as a credit against income tax, if that excess was withheld by one employer. The employer must adjust the excess for the employee.