Answer:
Shrubs (A)
Step-by-step explanation:
Ecological food chain which comprises of organisms that feed on each other to derive energy begins with a set of organisms called autotrophs. Autotrophs are unique organisms because of their abiility to capture light energy from the sun and convert it to chemical energy by a process called PHOTOSYNTHESIS. These autotrophs are called PRODUCERS in ecology.
Plants which includes shrubs are the common terrestrial producers. Energy is transferred from one trophic level to another. Plants convert only a little fraction of solar energy. Organisms called consumers feed on these plants (shrubs) and gain lesser energy than the one converted by plants because the plants has also lost some of this energy during their life processes.
Due to the fact that energy is used up at each trophic level of the food chain, the energy obtained by each organism in a trophic level decreases from the bottom up. I.e. from primary producers to tertiary consumers.
In a nutshell, the shrubs, which are the primary producers has the highest energy available (converted) for its use and it gets it directly from the sun.