Please Use the Following Information to Answer the Questions Below

Multiple Choice

Please use the following information to answer the questions below.
A scientist conducts an experiment to quantify the effect of mycorrhizae and soil nitrogen levels on plant growth in a grassland.The experiment has four treatments: (1) mycorrhizae present and ambient levels of nitrogen, (2) mycorrhizae present and nitrogen added, (3) mycorrhizae absent and ambient levels of nitrogen,and (3) mycorrhizae absent and nitrogen added.After four weeks,the scientist removes the aboveground plant material for weighing.
Figure 42.4
-What is the dependent variable in the experiment shown in Figure 42.4?

A) net primary productivity
B) total biomass of heterotrophs
C) net secondary productivity
D) total biomass of autotrophs