Question

what are the electrons going to move through (a series of what)?
lipids
enzymes
ribosomes
proteins

Explanation:

In biological electron - transport chains, electrons move through a series of proteins. Proteins in the electron - transport chain act as electron carriers. Enzymes are a type of protein but the more general and correct term here is proteins as a whole set of electron - carrying proteins are involved in electron transfer processes. Lipids are mainly for energy storage and membrane structure, and ribosomes are for protein synthesis and not directly related to electron movement in this context.

Answer:

D. proteins