Historically,what Movement Most Influenced Unionization in American Health Care Agencies/hospitals

Historically,what movement most influenced unionization in American health care agencies/hospitals?

A) Immigration laws protected foreign employees from discrimination in hiring or discharge based on national origin and citizenship status.
B) Women entered the workforce,gaining voice to support unions.
C) The Industrial Revolution led to poor working conditions and the need to protect workers.
D) Nurses were exposed to communicable diseases,which led to death and disability.