Choice "C" is correct. Under FICA, wages are compensation for labor. Reimbursed travel expenses are not considered wages and are not in gross income; therefore they are not subject to FICA.
Choice "b" is incorrect. Under FICA, wages are compensation for labor. Thus, contingent fees would be considered as wages.
Choice "d" is incorrect. Under FICA, wages are compensation for labor. Thus, bonuses would be considered as wages.
Choice "a" is incorrect. Under FICA, wages are compensation for labor. Thus, commissions would be considered as wages.