Consider the Phylogeny Below

Consider the phylogeny below. The coelom evolved once in the common ancestor of protostomes and deuterostomes. What does the phylogeny indicate about the lack of a coelom in flatworms (Platyhelminthes) ?

A) The trait for coelom is marked in that specific location on the tree so that it doesn't have to be drawn in for all the taxonomic branches that actually have a coelom.
B) Flatworms are very thin and difficult to dissect; identifying a coelom would be difficult.
C) The ancestral trait was for the presence of a body cavity; it was subsequently lost in some lineages.
D) The ancestral condition for protostomes is actually no body cavity, but because these are triploblastic organisms, it doesn't make sense to specify lack of a body cavity in the common ancestor.