Final answer:
A somatic mutation refers to a mutation that occurs in cells other than reproductive germ cells. A mutation in an adult nerve cell is an example of a somatic mutation.
Step-by-step explanation:
A somatic mutation refers to a mutation that occurs in cells other than reproductive germ cells, such as egg or sperm cells. These mutations are confined to just one cell and its daughter cells, and they cannot be passed on to offspring. Therefore, the correct answer is (C) a mutation in an adult nerve cell. This is an example of a somatic mutation because it occurs in a non-reproductive cell of an adult organism and does not affect the genetic material that could be passed on to future generations.
On the other hand, a mutation in an embryonic muscle cell would be considered a somatic mutation as well, but it is not listed as one of the options. A mutation in a sperm cell, on the other hand, would be a germline mutation, as it can be passed on to offspring. Lastly, option D is incorrect because it includes both somatic and germline mutations.