Which of the Following Factors, When Used to Label the Horizontal

Multiple Choice

Which of the following factors, when used to label the horizontal axis of the accompanying graph, would account most directly for the shape of the plot?

A) spongin concentration (gm/unit volume)
B) rate of cribrostatin synthesis (molecules/unit time)
C) number of pores per sponge
D) number of spicules per sponge
E) number of choanocytes per sponge