Final answer:
Crude density is the most basic measure of population density, representing the number of people per unit area of land. Physiological population density considers the number of people per unit area of arable land, while demography studies population changes over time.
Step-by-step explanation:
The most basic measure of population density is crude density, which is the calculation of the number of people per unit area of land. So, the correct answer to the question is option a) Crude. Crude density provides a general measure of the number of individuals living in a given area, such as a square kilometer or mile, and does not account for the variability in land use or quality, as urban or rural densities might.
Population density just represents the average number of individuals per unit of area or volume. In contrast, physiological population density is the number of people per unit area of arable land, which is land suitable for agriculture. Understanding these various measures of density can aid in assessing the distribution and pressure that human populations exert on the land they inhabit.
Furthermore, concepts like demography add another dimension to the study of populations by considering birth rates, death rates, and life expectancies, which are critical in understanding population dynamics over time.