Answer: The Answer's C.
Explanation: The structures that go from biggest to smallest follow the organizational rules of the Body. From largest to smallest, the chain goes as follows: Body system, Organ, Tissue, Cells, Chromosomes, Genes. So, following that chain, the stomach is considered an organ, so it goes first. Then the next largest item on the list is a cell, then a Nucleus that holds the chromosomes, then the chromosomes themselves that are made of genes, the smallest item on the list.