Except for identical twins, all the other human beings are genetically distinct from each other. why is this true?
a) environmental effects
b) migration
c) sexual reproduction

C) sexual reproduction

Explanation:

In sexual reproduction, genes from two different beings are mixed and create a new individual from the mix of those two polls of genes, that means that every new individual that is born by sexual reproduction, is in fact the mix of two predecessors, so we can´t have two individuals with the same genes, not even brothers, cause even brothers have different genetics cause of the way that the genes are mixed.

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.

burning fossil fouls really decrease the carbon in the atmosphere so b