Refer to the Graph

Multiple Choice

Refer to the graph. In the key, "elevated" refers to the addition of CO₂ above ambient levels, and "fertilized" refers to the addition of nitrogen fertilizer to the soil.Based on these data, can one conclude that nitrogen fertilizer enhances the effect of increased CO₂ on NPP in the forest?

A) Yes; NPP increases when both CO₂ and nitrogen are added but increases much less when only CO₂ is increased.
B) Yes; NPP increases under both elevated conditions but not under either ambient condition.
C) No; that information is not included in the data shown in the graph.
D) No; NPP increases when nitrogen is added but not when CO₂ is added.
E) No; NPP increases when CO₂ is added but not when nitrogen is added.