Geography is literally 'the study of Earth' from 'ge (γη)' meaning earth and 'grapho (γραφω)' to write or to study.
The ninth planet is Pluto, but this was ruled a dwarf planet in 2006. It has a small surface area than Russia.
Pacific Plate. The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres (40,000,000 sq mi), it is the largest tectonic plate. The Pacific Plate contains an interior hot spot forming the Hawaiian Islands.
For humans, population density is the number of people per unit of area, usually quoted per square kilometer or square mile (which may include or exclude, for example, areas of water or glaciers). Commonly this may be calculated for a county, city, country, another territory or the entire world.
The answer is b. Air pollution
