What is one reason why the classification of protists in one kingdom is difficult?

A.
Some protists are unicellular while other protists are multicellular.

B.
Protists more closely resemble members of other eukaryotic kingdoms than they do other protists.

C.
Protists may be funguslike, plantlike, or animal-like, but they do not have characteristics of more than one of these groups.

D.
Because they are unicellular, protists fit better in the two domains of prokaryotes.