Answer:
a) a census
Step-by-step explanation:
A census gives a good knowledge of the distribution of the population of a country.
Census is the head count of all the people living in a country at a particular period of time.
This head count provides a periodical count of the total population of a country. As this entails geographically determining the number of people living within a particular place, we can have a perfect knowledge of how the population of a place is perfectly spread out within a region.