Final answer:
Producers, specifically photosynthetic organisms like plants, make up the first trophic level in most terrestrial food chains.
Step-by-step explanation:
The type of organisms that make up the first trophic level in most terrestrial food chains are c) Producers (Plants). These photosynthetic organisms, such as plants and phytoplankton, use energy from the sun to produce their own food through photosynthesis, serving as the basis of the food chain. These primary producers provide energy and nutrients to subsequent trophic levels, starting with herbivores (primary consumers), then carnivores (secondary consumers), and so on up the food chain to apex consumers.