21. Which is correct about epigenetic regulation? (A) DNA methylation is a forever marker on genomes for gene repression. (B) The histone acetylation would compact the nucleosome structure for gene repression. (C) The N-terminus of histones contains many amino acids with positive charges such as asparagine and glutamine. (D) The gene expression can be switched on and off by the histone acetyltransferase and the histone deacetylase, respectively. (E) All amino acids of histones with methylation result in gene silencing.