Which of These Can Be Concluded from the Figure Below

Multiple Choice

Which of these can be concluded from the figure below?

A) In some years of the study the mean poison ivy biomass decreased to the level it was at the beginning of the study.
B) There were more elevated CO₂ plots than control plots.
C) Not all of the increase in mean poison ivy biomass can be attributed to the CO₂ that the researcher added.
D) Poison ivy in the experimental plots was more toxic than that in the control plots.