a nucleus a cell membrane a circular chromosome a mitochondrion
I gave my students this multiple choice question: Which cellular structure do organisms in the kingdoms Eubacteria, Archaebacteria, and Protista have in common?

Only one answer is correct among these 4 choices:
- a nucleus
- a cell membrane
- a circular chromosome
- a mitochondrion

Could you tell me which one is correct?

a cell membrane