A) net primary production.
B) secondary production.
C) gross primary production.
D) always less than that of heterotrophs.
E) none of the above

A) NO₃^2-
B) CO₂
C) SO₄^2-
D) H₂S
E) none of the above

A) could only have happened on land.
B) led to more complex life forms.
C) led to the evolution of cyanobacteria.
D) arose at deep hydrothermal vents.
E) none of the above