Question

which best explains how railroad companies were able to standardize their timetables in 1883? by combining into a single railway company by working together voluntarily by unionizing their labor forces by complying with federal legislation

Explanation:

In 1883, railroad companies standardized their timetables by voluntarily working together. There was no single - company merger, unionizing labor forces was not related to timetable standardization, and there was no federal legislation at that time for this purpose.

Answer:

by working together voluntarily