In engineering, the first step is to define the problem. Give an example of what you think an engineering problem dealing with the environment, plants, or animals might look like. ??​

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.