Respiratory system, circulatory system, what stuck, digestive system, and how do they work together?

Asap many people try to eliminate fat from their diets which is one reason it is necessary for humans to eat fat a) fat is the only way to get energy b) every cell in the body must contain fat c)fat stores less energy than polysaccharides d) saturated fats make blood vessels healthier

Agroup of organisms that changes over time is said to

Why are human population trends difficult to predict?