The figure below shows the results of a study to determine the effect of soil air spaces on plant growth.

-The best conclusion drawn from the data in the above figure is that the plant

A)grows best without air in the soil.
B)grows fastest in 5-10% air.
C)grows best at soil air levels above 15%.
D)does not respond differently to different levels of air in the soil.
E)would grow to 24 grams in 40% soil air.