33. Which of the following statements about epigenetic modifications are correct?a. Epigenetic modifications are not influenced by underlying DNA sequenceb. Epigenetic modifications are stable over timec. X-chromosome inactivation occurs in female mammal onlyd. DNA methylation always negatively correlated with gene expression on the promoter regions of a gene.e. Epigenetic modifications can be influenced by the environmental factors, such as nutrition.(A) a, b, d, e(B) e only(C) a, b, c, d, e(D) a, d, e