Scientists once classified protists based on whether they had plant-like, fungus-like, or animal-like characteristics. Why was this system problematic?

A. Nearly all protists actually are members of the plant, fungi, or animal kingdom. B. Many protists do not have the characteristics of any of the three groups.

C. All protists are too similar to each other to be classified in different groups.

D. As single-cell organisms, protists can't have characteristics of these groups.