How Did François Lutzoni and Marc Pagel Conclude That the Entire

How did François Lutzoni and Marc Pagel conclude that the entire genome of mutualistic fungi evolved faster than the genome of free-living fungi?

A) They based their estimate on the branch lengths in the phylogeny of a single gene.
B) They compared the evolutionary rates of multiple genes.
C) They conducted a genome scan at a great number of variable loci using microarray technology.
D) Their "conclusion" is mere speculation and is not backed by data.