D. All of the above.
Step-by-step explanation:
Low wages, long workdays, and poor working conditions are all causes of labor strikes.
During this time, workers were being treated terribly. The government would favor large corporations and businesses instead of the people, so they would not listen to their complaints or what they had to say. The wages were very low, some people barely earning enough money to feed their families. The workdays were long, this was before the 8-hour workday. Working conditions were poor and dangerous, many people often getting hurt or killed on the job. If someone got hurt on the job, the business would simply fire them, as they saw people as interchangeable cogs, easy to be replaced.
All of these factors caused labor strikes and labor unions, workers who wanted better for themselves and for other working people. If there was a labor strike, many people would stop working until the business did something about it. Most of the time this did not work, as I stated before, businesses saw them as easily replaceable. They would often fire the workers who were on strike and hire other people. This caused a lot of African Americans to be able to obtain jobs, as the white workers who were the first choice were on strike.