The answer is A. Energy
Step-by-step explanation:
B. Proteins are a structural component: they provide structure and support for cells. On a larger scale, they also allow the body to move.
C. Antibodies are made of proteins: they bind to specific foreign particles, such as viruses and bacteria, to help protect the body (inmune system)
D. Signaling: signal transduction pathways, which control the response of cells to various environmental signals, are mediated by the function of signaling proteins that interact with each other and activate one other with high specificity.