Observe the given graph representing the species-area relationship...

The given graph represents the species-area relationship proposed by Alexander von Humboldt.

In this graph:
The y-axis (Label A) represents Species richness.
The x-axis (Label B) represents Area.
The curve (Label C) represents the relationship on a normal scale, which is a rectangular hyperbola given by the equation $S = cA^z$.
The straight line (Label D) represents the relationship on a logarithmic scale, given by the equation $\log S = \log c + z \log A$.

Therefore, the correct matching is:
A $\rightarrow$ II (Species richness)
B $\rightarrow$ I (Area)
C $\rightarrow$ III ($S = cA^z$)
D $\rightarrow$ IV ($\log S = \log c + z \log A$)

Answer: A-II, B-I, C-III, D-IV