Compare the similarities and difference between anaerobic respiration in animal and yeast cells.​

Anaerobic bacteria can sustain itself without the presence of oxygen. Almost all animals and humans are obligate aerobes that require oxygen for respiration, whereas anaerobic yeast is an example of facilitative anaerobe bacteria.

b. the carbon cycle ensures living things have a source of hydrogen

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.