The Graph Below Is of an Index of Diversity of Arthropods

The graph below is of an index of diversity of arthropods in three different plots of a cornfield. In one of the three plots an insecticide was sprayed. Answer the questions below about this situation.
Arthropod diversity in three cornfield plots.
-The fact that the lines generally rise from left to right indicates

A) some species were disappearing as others were appearing.
B) time has passed since the experiment began.
C) in general, species diversity increased over time.
D) in August there were fewer insects than in any other month.