Final answer:
Membranes are found in all living cells, including animal cells, plant cells, and prokaryotic cells, but not in non-living structures like viruses.
Step-by-step explanation:
Membranes can be found in all living cells, which includes animal cells, plant cells, and prokaryotic cells. These cells all share common components such as a plasma membrane, cytoplasm, DNA, and ribosomes. Viruses, however, are not considered living cells and do not possess a cellular structure, thus lacking a cell membrane. Therefore, the answer to the question ‘Membranes can be found in all of the following except _________’ is ‘C) viruses’.