Refer to the Graph

Multiple Choice

Refer to the graph. The FACE experiment conducted in a North Carolina pine forest analyzed the effects of two factors on forest NPP.These two factors were

A) low and high levels of CO₂.
B) low and high levels of nitrogen fertilization.
C) levels of CO₂ and nitrogen fertilization.
D) levels of CO₂ and atmospheric temperature.
E) levels of nitrogen and atmospheric temperature.