What are two ways that the size of a population can increase ? what are two ways that the size of a population can decrease

For population increase two factors or ways are described which are birth or death, immigration and emigration.

The two ways a population can decrease is through mortality and emigration.

Explanation:

A population's increase is resolved  by  death, birth, immigration, and emigration. When a population's birthrate is higher than its death rate the population size, The population size is rises.

Also,The two factors responsible for the decrease in size of a population are emigration, which is the migration of an individual from a place. and mortality, which is the number of individual deaths in a population over a period of time.

option number one would be youre best option

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.