The right answer is Glucose (sugar).
The study of the growth of Saccharomyces cerevisiae (a yeast) populations on different media has established the heterotrophy of the yeast cell for carbon and its ability to produce biomass using extracellular glucose as the only carbon source. Population growth requires cells to perform biosynthesis (anabolism), division, active transport, internal vesicle movement ... all processes that require energy available in the form of molecules of ATP in which we find part of the energy extracted, by the catabolic processes, organic substrates.