Ag-protein receptor with gtp bound to it

the answer is:

carbon dioxide

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.

. ph changes the ability of them he enzyme to dissolve in water.

instead of copying and pasting things off of tests or work done on computer which im sure you did, try and read over the question carefully