Your Professor Wants You to Construct a Phylogenetic Tree of Orchids

Your professor wants you to construct a phylogenetic tree of orchids. She gives you tissue from seven orchid species and one lily. What is the most likely reason she gave you the lily?

A) to see if it's a cryptic orchid species
B) to serve as an out-group
C) to see if the lily and the orchids show all the same shared derived characters synapomorphies)
D) to see if you were paying attention