What is the drag force, buoyancy force, and gravitation force on a grain in motion?

Drag Force - A drag force is a force of friction caused by a body's movement through fluid like water, air etc.

Buoyancy force  - Buoyancy or upthrust force is an upward directed force imposed by a fluid opposing an object's weight

Gravitation force - Gravitational force is a force of attraction that draws mass from any object.

Explanation:

Drag Force - A drag force is a force of friction caused by a body's movement through fluid like water, air etc. Drag force functions contrary to direction of the current flow speed

Buoyancy force  - Buoyancy or upthrust force is an upward directed force imposed by a fluid opposing an object's weight. Due to weight of the fluid, pressure rises with depth in a section of fluid.

Gravitation force - Gravitational force is a force of attraction that draws mass from any object.

d. stage 4

explanation:

the existence of some kind of demographic transition is widely accepted in the social sciences because of the well-established historical correlation linking dropping fertility to social and economic development.[1] scholars debate whether industrialization and higher incomes lead to lower population, or whether lower populations lead to industrialization and higher incomes. scholars also debate to what extent various proposed and sometimes inter-related factors such as higher per capita income,lower mortality, old-age security, and rise of demand for human capital are involved.[2]

a. european colonies