So this question asks us, which of the following statements best describes developmental psychology? Let's run through them and see what we have. Statement A reads, "A field of psychology that focuses on mental processes like memory, attention, problem-solving," is definitely not it, so we're going to cross that off. Statement B reads, "A field of psychology that focuses on how psychological phenomena change over the lifespan and examines when, why, and how those changes take place," a lovely description of developmental psychology. So it's looking like our answer is B.
Let's just quickly read through C and D to make sure that we understand why they are incorrect. So, C is a field of psychology that focuses solely on children. Remember, developmental psychology considers the entire lifespan, not just childhood, although that is a very large part of the field. So that is why C is incorrect. And then D is a field of psychology that focuses on how stimuli and reinforcement can shape behavior.
That is sounding very behaviorism-like, isn't it? So that is why D is incorrect. And our answer here is B. And there you go.