Answer:
a. consuming organisms at a lower trophic level.
Step-by-step explanation:
A food chain shows how various organisms are related to each other as per the food they eat. Each level of a food chain refers to a distinct trophic level.
Food chain is basically related to transfer of matter and energy from organism to organism in the form of food.
In a food chain, consumers gather energy by consuming organisms at a lower trophic level