Infertility is usually defined as: select one: a. childlessness. b. the inability to conceive after one year of unprotected intercourse. c. the inability to conceive after ten years of unprotected intercourse. d. sterilization.

I believe the answer is: b. the inability to conceive after one year of unprotected intercourse

In united states, the rate of infertility among women is around 12% and 15% among men .The most common causes of infertility, are :low sperm count, improper temperature within the female host's body, and hormonal imbalance in the host's body 

The correct answer is a. when they started making tools that will them in cultivating lands, they could raise crops and that made them attached to one place for a longer period of time. after that, they started domesticating animals and building their own permanent settlements that resemble the ones we have today.