As estrogen and testosterone levels fall in later life, the frequency of intercourse and the frequency of sexual fantasies

As estrogen and testosterone levels fall in later life, the frequency of intercourse decline or decrease and the frequency of sexual fantasies also decrease or decline.

The sex hormones have an impact and regulate or direct the male and female physical development of the sexual characteristics. The hormones testosterone and estrogen are present both in males and females but the males have higher testosterone levels and females have higher estrogen levels.

In humans the hormones impact the sexual behavior at a lower level once the sufficient level of hormones is present. In the later part of life, with the decline in level of the sex hormones the frequency of intercourse as well as the sexual fantasies decline.

substitution is the answer in this case

b. lithosphere, asthenosphere, mesosphere   is the answer most likely