a. Reproducing
d. maintaining structure
f. obtaining energy
These three traits definitely standout as a challenge for every living creature in the ecosystem. In Darwin’s Natural Selection Survival of the fittest: being fit is one category in order to survive the wild, in other words, being flexible. Reproduction is battle royale in both humans and animals, even for plants too. Why? Because the ecosystem changes, the weather changes, the food chain is a combat to chase. Some can’t even reproduce due to hereditary or physical causes. Energy is as important as living. If plants can make their own food how about the carnivores and the omnivores. Food is a challenge. Structure is sustaining the capacity and ability to hunt and survive. Important and a by-product of obtaining energy.