30. Which one described below is true for post-translational modification (PTM) of proteins?(A) Phosphorylation but not dephosphorylation plays an important role in signal transduction.(B) The activity of histone can be regulated by methylation but not acetylation at its lysine residue.(C) The conformation and also biological activity of protein can be regulated by PTM.(D) Ubiquitination would decrease the molecular weight (size) of protein.