(D) is incorrect because it states that exercise can "DIRECTLY" lower blood pressure. However, the passage gives us a chain of events in which exercise can calm minds which can reduce stress which can lower blood pressure. Therefore, engaging in exercise can only INDIRECTLY lower one's blood pressure.
It is also important to note that the question is looking for the answer choice that is "most strongly supported" by the passage. While (D) may not feel that far off base, (E) is a much safer answer.
Does that make sense? Please reach out with any other questions and best of luck with your studies!