This type of relationship occurs when individuals of one species are dependent upon individuals of another species for survival.

• A. Mutualism
• B. Commensalism
• C. Parasitism
• D. Symbiotic

Answer: (D)

Symbiotic relations are close, long‑term interactions between two different species where at least one partner relies on the other for survival. That idea fits this statement because it’s about a connection so essential that the species depend on each other in some way. All the other terms describe specific kinds of these relationships: mutualism is when both benefit, parasitism is when one benefits at the expense of the other, and commensalism is when one benefits and the other is not helped or harmed. The word that best covers the idea of an enduring, dependent association is symbiotic, since it includes these different forms of cooperation or dependence. For example, pollinators and flowering plants rely on each other (a mutualistic, dependent relationship); a parasite and its host rely on each other for nutrients; and some symbiotic pairs only benefit one side without harming the other, yet still show this close, interdependent connection.