Final answer:
For both men and women, as they age, reproduction becomes less likely due to declines in fertility and decreases in sex hormone levels.
Step-by-step explanation:
For both men and women, as they age, reproduction becomes less likely (C). As women approach their mid-thirties, their fertility gradually declines until it diminishes completely at menopause. Menopause is marked by the cessation of the menstrual cycle, which happens due to the loss of ovarian follicles. The average age for menopause typically ranges between 50 and 52 years, but it can vary depending on factors such as overall health and lifestyle.
Meanwhile, in men, fertility also declines with age. While men can continue to produce sperm into old age, the quantity, quality, and motility of their sperm decrease. Testosterone levels decline, a condition referred to as andropause, which can sometimes affect sperm production, though this usually does not occur until much later in life.