Which One of the Following Has Been an Underlying Reason

Which one of the following has been an underlying reason for the growth in benefits over time?

A) The tax treatment of benefits programs is favorable for employers than the tax treatment of wages and salaries.
B) The similarity in benefits provided to all employees to avoid differentiation.
C) The fall of organized labor from the 1930s through the 1950s.
D) The range of benefits change in correspondence to change in wage and price controls.
E) The cost advantage that groups typically receive over individuals.