Final answer:
STIs are included in discussions of the male reproductive system because they affect both male and female reproductive systems, potentially leading to significant health issues and loss of fertility in males.
Step-by-step explanation:
The inclusion of sexually transmitted infections (STIs) in discussions of the male reproductive system is pertinent because STIs can significantly affect both male and female reproductive systems. The correct answer to the question 'Why do you think that STIs are included in the male reproductive system?' is B. STIs affect both male and female reproductive systems. STIs can lead to reproductive health issues in males, including infections of the urethra, testes, prostate, and epididymis. These infections may be asymptomatic or cause a range of symptoms that can lead to severe morbidity and a loss of fertility.