Final answer:
All protists are eukaryotic, meaning they have a nucleus. They are a diverse group including protozoa (animal-like), and can be unicellular or multicellular, but not all are heterotrophic, flagellated, or have a mineral test.
Step-by-step explanation:
All protists are alike in that they are eukaryotic, which means they have a nucleus within their cells. Additionally, protists are incredibly diverse organisms that can be animal-like, plant-like, or fungi-like. Animal-like protists, or protozoa, are heterotrophic and can move, but not all protists are heterotrophic or motile. Furthermore, while most protists are unicellular, there are instances of multicellular protists, such as kelp. It is also not true that all protists are flagellated or have a protective mineral test (a kind of skeleton). Hence, of the characteristics listed, the one that is common to all protists is that they are eukaryotic.