Final answer:
The Federal Government between 1865 and 1900 was generally hostile towards labor unions, often siding with industry over workers in disputes such as the Great Railroad Strike of 1877, option A.
Step-by-step explanation:
Between 1865 and 1900, the general attitude of the Federal Government concerning labor unions was primarily hostile toward union efforts to improve workers' conditions. This hostility was displayed through various reactions, including the crushing of the labor movement, the use of government agents to suppress strikes, and the implementation of measures such as the Sherman Anti-Trust Act and other regulations which were mainly aimed at controlling corporate power but also affected labor unions indirectly. Notable incidents showing the government's stance include the Great Railroad Strike of 1877, where the government intervened to support the interests of industry over the laborers.