The molecular structure of DNA is not static. Under the influence of various physical and chemical factors or environmental factors, the sequence of the base pairs on D. NA. , that is, the genetic code, may change, causing genetic mutations. Even under normal conditions At the same time, extremely low-frequency mutations also occur during D. NA. replication. This passage mainly supports the argument that:. ['DNA molecular structure is highly variable.', 'DNA may be mutated.', 'DNA is very prone to genetic mutations.', 'DNA variation is possible only in special cases.']