The correct answer is B. They must contain a nucleus
Step-by-step explanation:
One of the characteristics that make eukaryotes different from prokaryotes is that eukaryotes contain membrane-bound organelles including a nucleus, which is the organelle that controls most functions in the cell. Besides this, eukaryotes have other organelles such as lysosomes or Golgi apparatus, while prokaryotes lack these organelles. Moreover, prokaryotes are unicellular while eukaryotes can be unicellular or multicellular. Thus, the correct statement of eukaryotes but not of prokaryotes is "they must contain a nucleus".