Homeostasis is an organism's ability to maintain its internal conditions even if the external environment changes. How does the paramecium use active transport (contractions) to maintain
homeostasis?

Explanation is in the file

tinyurl.com/wtjfavyw

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.