Controlled population growth.
Explanation:
US is a highly developed country and it has expansive infrastructure and highly mechanized agricultural equipments. So first option is not a choice. Second, access to chemical fertilizers and pesticides in a country with such advanced agriculture infrastructure is very easy. Third US is well known for using GM crops.
US does not have a controlled population growth because if not the birth rate then migration of people to US is a major concern for that country. Thus, this will be a correct choice for the given question.
A stem cell is a cell that has layers of bacteria that helps protect the water that follows through it.
Answer:
natural selection is animals slowly adapting to its environment
an example is giraffes, giraffes with longer necks will be able to consume more food than giraffes with shorter necks as they they can reach for the leaves on trees. over time the giraffes with shorter necks become extinct and giraffes with longer necks still remain.
