Final answer:
Epigenetic changes are modifications that do not alter the DNA sequence but affect gene expression and can be influenced by environmental factors; some of these changes are also heritable.
Step-by-step explanation:
The correct response to the question regarding the nature of epigenetic changes would be 'They can be influenced by environmental factors'. Epigenetic changes are modifications that affect gene expression but do not change the DNA sequence. These changes can include the addition or removal of chemical groups to the DNA molecule itself or to histone proteins associated with DNA, which can alter the accessibility of genes to the transcription machinery and thereby influence whether those genes are expressed ('turned on') or silenced ('turned off'). Environmental factors, such as diet, stress, and exposure to toxins, can lead to epigenetic changes. Furthermore, some epigenetic changes are indeed heritable, meaning they can be passed down from one generation to the next.