Which class of animals has a single compartment "simple" stomach?

The correct answer is monogastrics, which refers to animals that possess a single-compartment stomach. This type of stomach structure allows for a straightforward digestive process where food is broken down primarily through enzymes and acids rather than through fermentation. Animals such as pigs, horses, and humans belong to this category.

Monogastrics have adaptations that allow them to efficiently digest their food without the necessity for extensive fermentation, which typically occurs in more complex stomach systems like those found in ruminants. Ruminants, in contrast, have a multi-compartment stomach designed specifically to break down fibrous plant material through a specialized process involving microbial fermentation. Herbivores can be either monogastric or ruminant, and not all herbivores have a single-compartment stomach. Insectivores typically have a simple stomach structure as well, but this group specifically refers to animals that primarily feed on insects.

Thus, the defining characteristic of having a single-compartment stomach aligns clearly with monogastrics, making this option the most accurate choice.