15. Fossil fuel is one of the primary sources of
A) oxygen
B) nitrogen
C) carbon dioxide D) phosphorus
16. The primary source of phosphorus is:
A) Plants
B) Animals
C) rocks
D) sun
17. The process whereby water is converted from a gaseous state to a liquid state is called
A) precipitation B) evaporation C) condensation D) sublimation
18. What is the process of releasing free nitrogen in the air?
A) nitrification B) evaporation C) denitrification D) ammonification
19. Which of the following could be a good source of organic phosphate?
A) water
B) stones
C) animals
D) sun
20. In photosynthesis, plants give off:
A) Carbon dioxide B) oxygen
C) hydrogen
D) carbon​