Given that a blowfly starts its lifecycle only if there are appropriate conditions met, one of which is suitable temperature, the correct answers as to what can impact the timing of the blowfly lifecycle is the air temperature.
I don't see how humans will impact when this fly is going to be born, so A and C are incorrect. Leaves also doesn't really affect blowflies, which is why D is incorrect as well.
The correct answer is option A. Carrying the genetic code and determining an organism's structure and function are the functions of DNA. It is the hereditary material in almost all other organisms. The information in a DNA is stored as codes that is composed of chemical bases.
Natural selection can only occur because of a variety in a population. Natural selection refers to environmental factors that affect a population and causes some of the population to have more surviving offspring than others. An example is a giraffe with a longer neck will be more likely to survive and reproduce (as it can gather more food from taller trees)