The figure below shows the increase morphological complexity in crustacean legs in 12 different ...

The figure below shows the increase morphological complexity in crustacean legs in 12 different phylogenetic comparisons. Why did the authors of this study choose to analyze the data independently for each compari-son?
 
  a. The lower sample size in each comparison makes for a more powerful statistical test.
  b. This methods allows to test for lineage sorting within each of the 12 comparisons.
  c. The observed pattern allows them to exclude lineage sorting as a possible evolutionary mecha-nism.
  d. This method controls for phylogenetic correlations.