Which of the following factors can affect human fertility?

The correct choice highlights several key factors that influence human fertility: age, hormone levels, health, and lifestyle factors all play significant roles.

Age is crucial in fertility; women are generally most fertile in their 20s and early 30s, after which fertility declines. For men, while they can remain fertile longer, advancing age can affect sperm quality.

Hormone levels directly influence reproductive functions. In women, hormones regulate the menstrual cycle and ovulation, while in men, hormones like testosterone are vital for sperm production. Any imbalance in these hormones can lead to fertility issues.

Health status is also critical. Conditions such as obesity, diabetes, or sexually transmitted infections can impair fertility. Chronic illnesses and certain medications might have negative effects on reproductive health as well.

Lifestyle factors, including diet, exercise, substance use (like alcohol and tobacco), and stress management, can significantly impact fertility. A healthy lifestyle generally promotes better reproductive health, while poor lifestyle choices can lead to fertility struggles.

The other options, while they touch upon social and environmental aspects, do not directly connect to the biological and physiological factors that distinctly affect human reproductive functions as outlined in the correct choice.