As seen in the video game death stranding.
Two extinction level events happened and wiped out half of all human life. Building and cars and homes were destroyed and replaced by growling grass or dirt. A new species of bug came about called a cryptobite and a bridge was formed between the world of living and dead and hence forth came the rise of beached things
Lipids would be the answer that you are looking for. When talking food energy it's best to speak in terms of calories. Therefore, lipids or fats offer the greatest amount of heat or energy.
A hydrogen bond connects the nitrogenous bases of the nucleotides together!
Natural selection means that the organisms better adapted to their environment, that is, they have developed the right characteristics/skills/response to the external ambient, have higher chance to survive, making the next generations genetically inherit such acquired surviving characteristics.
These generations will thus have a higher chance of survival, making these species being "naturally selected" as survivors, while those who haven't or are slower in this process, have a higher risk of elimination.
D, think of it like a house.
