Where are cells that circulate through the immune system produced?

People who exercise for an hour may have lower cholesterol levels. is that a statement? a law? or a hypothesis?

Which would happen if more forests were cut down? a. the nitrogen cycle would be stopped b. nitrogen would be fixed by bacteria more quickly c. the amount of co2 in the atmosphere would increase d. fossil fuels would build up in the soil c the amount of co2 in the atmosphere would increase

What would happen if the krill were removed from the food web