The correct answer is D) welfare reform.
What was not a cause for labor strikes and sit-ins in the early 1900s was welfare reform.
The Welfare Reform was the series of federal laws that tried to improve the United States social warfare programs. The Welfare Reform aimed to reduce the number of people that depended on assistance programs of the government. The idea was to help these people to be self-sufficient. What indeed were causes for labor strikes in the early 1900s were higher wages, the 8-hour day, and workplace safety.