Imagine That a Clade of Sulfate-Respiring Heterotrophs in the Ocean

Imagine that a clade of sulfate-respiring heterotrophs in the ocean evolved complex multicellularity. How likely is this new clade to colonize the land surface successfully?

A) very likely, as animals, plants, and fungi all became successful on land
B) not very likely, as the land surface is already saturated with multicellular organisms
C) very likely because colonists that exploit a resource (sulfate, in this case) not much used by existing land organisms will prosper
D) not very likely, as air does not contain sulfate