Final answer:
Voluntary standards have evolved over time, often in a non-linear, iterative process that includes various stages such as planning and revising. Option 'a' is the closest match, suggesting standards generally 'Risen steadily since World War II' as they adapt to new field experiences and add more detailed requirements.
Step-by-step explanation:
The question pertains to how voluntary standards have developed over time, particularly since World War II. None of the provided options are directly applicable because the development of voluntary standards often follows an iterative and organic process influenced by new experiences and knowledge in the field. However, if we must choose an option most reflective of the historical trend, 'a. Risen steadily since World War II' might be the closest, as standards tend to evolve and become more detailed over time. This process can be simultaneously and maybe even haphazardly at times, which includes various stages such as planning, revising, editing, drafting, and then perhaps returning to planning. This dynamic cycle ensures the standards remain relevant and effective in their respective fields.