Which type of growth occurs when population growth slows or stops after a period of exponential growth

Logistic growth occurs when population growth slows or stops after a period of exponential growth. In logistic growth, sigmoid growth curve(S-shaped) is produced.

At this period, the net increases and a decrease in the number of individuals is zero because the population reached its carrying capacity, as a result, the growth becomes constant.  Carrying capacity is the maximum number of individuals of a population an ecosystem can support.

As the population reaches its carrying capacity after exponential growth the growth curve becomes sigmoid which shows the environmental resistance is slowing down the growth rate.

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.

i don't know. if i were you, i would search it up online : d