Which of the Following Best Matches the Description

Which of the following best matches the description?
-The flow of carbon from the atmosphere to living organisms and back again.

A) denitrifying bacteria
B) herbivore
C) omnivore
D) producer
E) trophic level
F) community
G) ectoparasite
H) limiting factor
I) none of above
J) secondary consumer
K) nitrogen cycle
L) biomass
M) habitat
N) carbon cycle
O) interspecific competition
P) nitrogen-fixing bacteria
Q) intraspecific competition