Why can’t food chains go on forever?

Because at some point in that food chain, the energy consumption has it's limit, and the predator will not have anything to hunt it. There is a limited amount of energy in a food chain that can go around, and once you reach the predator, that energy doesn't quite run out but it hits that limit where the chain has to repeat itself.

Explanation:

answer:

sequence 1- deletion

                  2- duplication

                  3- insertion

                  4- substitute

                  5- inversion