What are epigenetic modifications?

a. the addition of reversible changes to histone proteins and DNA

b. the removal of nucleosomes from the DNA

c. the addition of more nucleosomes to the DNA

d. mutation of the DNA sequence

The first stage of controlling gene expression in eukaryotic cells takes place at the epigenetic level. Genes can be turned on or off by means of epigenetic mechanisms that regulate access to the chromosomal area. Chromatin remodelling regulates how tightly the DNA is coiled around histone proteins to govern how much DNA is crammed into the nucleus.

The term "around genetics" is epigenetic. The nucleotide sequence is unaffected and the modifications to the histone proteins and DNA are temporary. Instead, these modifications affect the chromosomal shape (open or closed) and are transient (although they frequently endure through numerous rounds of cell division). Depending on the position and DNA and histone protein changes, a gene might be activated or inactivated.

Therefore, the nucleotide sequence is unaffected and the modifications to the histone proteins and DNA only. So, the rest of the options are irrelevant.