Analogous structures
result from evolution in a similar environment
indicate a common ancestor exists between two organisms
are features which organisms still have but no longer use
develop when a mutation occurs in the dna of an organism

Answer is result from evolution in a similar environment

The analogous structures are the various structures in different species having the similar in function because face similar environmental pressure, but have different in their origin. These structures evolved separately. Thus, they do not share common ancestor. For example are wings of birds and wings of insects, fins of fish and flippers of whales. Analogous structure supports convergent evolution.

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).