<u>Answer:</u>
<em>C) Population Density Equation </em>
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<u>Explanation:</u>
Population density is the total population that has been divided by the total area of the land. "Demography" is the "statistical study" of populations. It includes the study of size, structure, and distribution of the population. There are both direct and indirect methods for the data collection. Direct data is vital that tracks all the births and deaths and also include the changes in the legal status such as marriage, divorce, and migration. On the other hand the "indirect method" is vastly dependent on the historical demography.
Waves tend to travel faster through a hot material than a cold material. The reason behind this is that heat makes the waves obtain more kinetic energy. Thus, temperature and speed is directly proportional. As temperature rises, the speed of wave also increases.