A

B. Most states had passed some safety laws, but enforcement varied.

Explanation:

In 1900, the workplace safety laws and occupational health measures were not enforced, which led to very a poor working environment. Many workers received minimum wage but were exposed to very high health and safety risks. No training and safety measures were implemented, which resulted in a high rate of deaths among the workforce. Statistics are shown in the graph below. As a result, some workers decided to leave their jobs to prevent injuries.
During that time, the majority of states had some safety laws, such as the Safety Appliance Act of 1893. However, such regulations did not apply to all existing problems and sometimes were implemented poorly.

Fatalities and incidents rates 1900-2000
Fatalities and incidents rates 1900-2000 (Source: www.injuryprevention.bmj.com)