The correct answer is B. Differences in the characteristics of individual trees
Explanation:
Evolution refers to the changes certain species of organisms experience over a long time that is mainly prompted by natural selection which occurs as changes in the environment or conditions make certain traits to prevail over time and others to disappear. This occurs in the case presented as drought makes trees with deep roots prevail over time while other trees disappear. This implies,s the factor that allows natural selection and evolution to occurs is the differences in the characteristics of individual trees or that some of the trees have deep roots that prevail while others with superficial roots tend to disappear.
Respiratory and circulatory systems work hand in hand to expel wastes. respiratory system removes CO2 and the circulatory uses the blood as a medium to move excess salts and water from source to sink.
