Having trouble and can you please explain

Ahill is made of rock particles of different sizes. which of these agents of erosion probably caused the hill to form?

What is the "great pacific garbage patch"? (a) a large area of marine debris concentrated by rotating ocean currents (b) a large area around the pacific rim where debris collects from natural disasters such as tsunamis (c) an area in the pacific ocean where trash is intentionally dumped due to lack of landfill availability (d) a large trash dump located in hawaii

Why is the study of demography important to geographers