Please help me with these ecology questions! Thank you

21. Fertilizers provide plants with
a. nitrogen.
b. carbon.
c. water.
d. oxygen.
22. Which of the following convert(s) nitrogen from air into a form plants can use?
a. bacteria
b. lightning
c. sunlight
d. both a and b
23. Plants use nitrogen to make
a. carbohydrates.
b. nitrogen gas.
c. amino acids
d. both b and c.
24. An animal returns nitrogen to the environment when it
a. breathes.
b. decomposes.
c. urinates.
d. both b and c.
25. Animals get phosphorus from
a. the air.
b. eating plants.
c. water.
d. the soil.
26. Phosphorus in the soil comes from
a. rocks.
b. decaying organisms.
c. the air.
d. both a and b