Final answer:
Methylation is a process that involves the addition of a methyl group to a molecule, and it can occur in various biological processes, including DNA methylation.
Step-by-step explanation:
Methylation is a process that involves the addition of a methyl group to a molecule. In biological systems, the common methylating agent is S-adenosylmethionine (SAM), which transfers a methyl group to acceptor molecules. Methylation can occur in various biological processes, including DNA methylation, where methyl groups are added to the DNA molecule, resulting in gene silencing. Therefore, the correct answer is 5) None of the above.