Which situation allows for evolution during gene duplication?
a. the original gene performs the same role as the mutated gene.
b. the original gene never duplicates.
c. a mutation occurs in one copy of the original gene.
d. existing genes are copied over generations.

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.

actually the answer is c