Final answer:
Labor unions were largely responsible for collective bargaining and the implementation of the 40-hour workweek, which have been significant changes to labor laws.
Step-by-step explanation:
Labor unions have been instrumental in advocating for changes that have significantly shaped labor laws in history. Two main historic changes attributable to the efforts of these unions are c) Collective bargaining and the establishment of the 40-hour workweek. Collective bargaining refers to the process in which unions negotiate with employers to reach agreements that govern labor conditions, salaries, and benefits. The implementation of the 40-hour workweek is a landmark labor standard that specifies the maximum number of hours an employee is expected to work per week at regular wages, ensuring that overtime pay is provided for extra hours worked.