Which one the following is statements is true?

a) exposure to antibiotics causes individual bacteria to mutate and become resistant

b) crossing over and random fertilization decrease variation

c) natural selection works on variation already present in a population

d) organisms evolve structures that they need

e) none of the above

D. Oraganism evolve structures that tjey need.. And the best example of this is evolution if giraffe neck.

currents is the correct answer.

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides