What is the main difference between catalysts
and enzymes?

Enzymes are proteins that increase (only) the rate of chemical reactions converting substrate into product.

Catalysts are substances that increase or decrease the rate of a chemical reaction but still remain unchanged.

google my dude. if it doesn't show up ask me.

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.