Human blood consist of blood groups a b in open however there is one more blood group ab which contains allies anb in the same genotype what is the phenomenon called

RH Negative Blood Type

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.

the electromagnetic energy from the sun arrives in the form of visible and invisible light.