Arrange the steps in the correct order to explain how a muscle fiber contracts. myosin and actin protein filaments attach to each other. calcium ions release into the myofibrils. myosin filaments pull on the actin filaments. the nerve impulse reaches the neuromuscular junction. the motor neuron carries the nerve impulse. the sarcomere shortens. ↓ ↓ ↓ ↓ ↓

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area

Which of the following can be reduced by the use of renewable energy sources? a. social costs b. economic costs c. environmental costs d. all of the above select the best answer from the choices provided a b c d

Phosgene is a chemical agent that is formed by decomposition of chlorinated hydrocarbon solvents by ultraviolet radiation. a. false b. true