Which of the following could be a possible cause of infertility for a couple visiting a fertility clinic?

Infertility in couples can arise from various factors, and the impact of radiation therapy on male reproductive health plays a significant role. In this case, the husband’s recent radiation therapy for a cancerous tumor on his femur could affect his fertility due to potential damage to his testicular function, sperm production, or even hormonal balance. Radiation can lead to reduced sperm count and motility, making it more difficult for the couple to conceive.

The other factors mentioned, while they can have implications for fertility, are not as direct as the effects of radiation therapy. For instance, high levels of alcohol consumption, as noted in the choice about the couple's drinking habits, can also negatively impact fertility by affecting hormone levels and sperm production in men, as well as ovulation and menstrual regularity in women. However, it is not as unequivocally linked to infertility as the consequences of radiation.

Marathon running and maintaining a healthy BMI generally do not pose fertility risks unless they lead to severe energy deficits or menstrual irregularities. A BMI of 21 is typically considered healthy for most individuals and should not inherently cause infertility.

In summary, the scenario relating to the husband’s previous radiation therapy is a clear and recognized factor that could lead to infertility, making it