When is facilitated diffusion necessary?
a. when the molecules are too large.
b. when the molecules are insoluble.
c. when the direction of movement is opposite to natural diffusion.
d. none of the above

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 thinking chemical change

c. establishing proper sleep hygiene

yes

no

blue is scattered more than other colors because it travels as shorter, smaller waves. this is why we see a blue sky most of the time.