Observe the graph and select the correct option:

The species-area relationship follows the equation: \[ S = C A^Z \] where:
- \( S \) is species richness,
- \( A \) is the area,
- \( C \) and \( Z \) are constants.
This equation, proposed by Alexander von Humboldt, suggests that species richness increases with area but not linearly.
In absence of fertilization, corpus luteum degenerates into __________.
Identify ‘A’ in the given graph of population growth. 