In which cells is DNA primarily found?

DNA is primarily found in all living organisms, regardless of the specific type of cell. This is because DNA serves as the genetic material that carries the information necessary for the growth, development, reproduction, and functioning of all forms of life. It is present in the nucleus of eukaryotic cells, which include the cells of plants, animals, fungi, and many microorganisms. In prokaryotic cells, such as bacteria, DNA is located in the cytoplasm since they lack a nucleus.

Each of the other options refers to specific cell types. Red blood cells, for instance, lose their nuclei as they mature, meaning they do not contain DNA. Nerve cells and skeletal muscle cells do contain DNA, but they are just examples of the many cell types across living organisms that carry DNA. Therefore, the choice indicating all living organisms encompasses the broader reality of DNA's existence across various life forms.