Checks and balances that maintain stable populations over time are called _______. There are _______ billion people on Earth as of the year 2020. The prediction is that the human population will reach about _______ people in 2050. A/An _______ is a group of individuals of the same species living in the same area. A/An _______ is a natural environment with specific characteristics and specific types of animals and plants. Four major types of pollution are _______, _______, noise, and _______ pollution.
