Payroll deductions
a. are amounts added to employees' gross earnings to determine their net pay
are voluntary
b. decrease the amount of cash an employee receives
c. are amounts subtracted from employees' gross earnings to determine their net pay
d. increase the amount of cash an employee receives

C. Are amounts subtracted from employees' gross earnings to determine their net pay

Explanation:

Employees most of the time have a gross and a net salary. Gross salary is the agreed upon amount that the employee should receive as compensation for their work, as should be written down in a contract. Net salary is the actual amount the employee receives, after payroll deductions, which are amounts held by the employer. These include local and federal taxes, pension fund contributions, child support payments, union fees, among others. Some of these are mandatory while others apply only for some workers.