12. is a form of artificially acquired immunity that occurs when the
majority of a population, but not all, has been given a vaccine and becomes
resistant to infection. It only works if the majority is vaccinated.

Your answer is a because that is true

In order to understand the problems of unwanted infertility in a country — the gambia — where the desire for children and the fertility is very high, a population-based survey was undertaken. all infertile women in 24 randomly selected enumeration areas were assessed. the study included a review of the problems faced and coping mechanisms employed by infertility clients and types of health care available for infertile couples in the different types and levels of the formal and traditional health system. half of the infertile couples failed to seek formal health care, and they have to reach a certain level of care in order to be properly managed. alternative care is often sought. child fostering is also a frequent solution to childlessness. in-depth interviews revealed that traditional care like healers and spiritual leaders are frequently consulted long before formal health care. this delay could be a problem in those cases where infertility is caused by infections.