Trophic levels refer to

The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. ... The word trophic derives from the Greek τροφή (trophē) referring to food or nourishment

Explanation:

i think it would be b. tissue because an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

really dont know just need some points