Which of the following is the most likely cause of infertility in men?

A) low sperm count
B) jogging
C) chlamydia
D) being too thin

Low sperm count is a common cause of male infertility, which can be caused by a variety of factors including hormonal imbalances, genetic defects, infections, and lifestyle factors such as smoking and drug use. Jogging or being too thin alone are not typically associated with infertility in men, while chlamydia can potentially cause infertility if left untreated due to its ability to damage the reproductive system. However, low sperm count is still more commonly associated with male infertility.