Answer:
belief in the afterlife.
Explanation:
Archaeologists have noticed that burying the dead in the ground has been a very old tradition but a special feature added to it during the river valley civilization was that some necessary items of daily life had been added to the grave to help them in their next life. We notice these practices among Sumerians, Mayans, and Harappans. Some historians also believed that underground burials the faith in the next world lies under the Earth and underground burials provide easy access to them.
In a population pyramid, the size of the population under investigation is depicted on the horizontal axis, and age is aligned on the vertical axis. The result is a series of bars stacked on top of one another, each representing an age category (typically in 5-year age groups), with the youngest age group represented by the bottom bar and the oldest age group by the uppermost bar. The horizontal length of each bar represents the number of individuals in the specific age group for the population depicted.
I think A is your answer, cause that's what pops out at me the most. Hope that helps XD