There exists a bidirectional relationship between sexual arousal and testosterone levels.Which of the following best describes that relationship?

A) Decreased testosterone levels can be a cause and a consequence of sexual activity.
B) Increased sexual arousal is related to fluctuations in testosterone levels.
C) Decreased sexual activity is directly related to variations in testosterone levels of men only.
D) Sexual arousal can be a cause and a consequence of increased testosterone levels.

Sexual arousal can lead to an increase in testosterone levels, and high levels of testosterone can also increase sexual arousal. This bidirectional relationship is important in understanding the role of testosterone in human sexual behavior. Option A is incorrect because sexual activity does not necessarily cause decreased testosterone levels in all cases. Option B is partially correct, but it only describes one direction of the relationship. Option C is incorrect as decreased sexual activity may not directly relate to variations in testosterone levels in men.