The best definition of a consumer among the options provided is:
B. Organisms that get food by eating other living things.
Consumers are organisms that obtain energy and nutrients by consuming other organisms.
They are also known as heterotrophs, as they rely on external sources of organic matter for their energy needs.
In contrast, option A refers to decomposers, which break down dead organic matter.
Option C describes decomposers and detritivores, which feed on dead organisms or organic waste.
Option D specifically refers to carnivores, which are a type of consumer that consumes other animals for food.