Answer:
B. People named full moon after things that were happening when the full moon happened like "Hunter's Moon"
Traditionally, people in the Northern Hemisphere spent the month of October preparing for the coming winter by hunting, slaughtering and preserving meats for use as food. This led to October's Full Moon being called the Hunter's Moon, Dying Grass Moon, and Blood Moon or Sanguine Moon.
D. People used to use moon phases as a type of calendar.