List the reasons why food chains do not tend to exceed four links

Due to loss of energy at each tropic levels.

Explanation:

Food chain may be defined as the sequential level of tropic levels in which the organisms eat other animals and itself being eaten by other animals. The plants acts as producers in the food chain.

The food chain is limited up to 3-4 tropic levels only. The energy is lost at each tropic level according to the 10% law of energy. The limitation of energy and its lost makes the food chain limited only up to few tropic levels. Instead of food chain, food web exist in nature.

preservation because he preserves part of the land and preserves means save

explanation:

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."