Which one of the following criteria is necessary for natural selection to occur

image result for how many calories of energy will 20 grams of carbohydrates provide in one gram provides 4 calories

consuming the right balance of protein, carbohydrates and fat can you maintain a healthy weight and optimize your energy levels. protein and carbohydrates both contain 4 calories per gram, while fat provides 9 calories per gram.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.