The Origin of Eukaryotic Membrane-Bound Organelles Other Than Mitochondria and Chloroplasts

The origin of eukaryotic membrane-bound organelles other than mitochondria and chloroplasts is a contested issue. Which of the following statements BEST describes why it is difficult to determine how structures like the nuclear membrane originated?

A) Because the first eukaryotic cells likely arose before the first fossil eukaryotes are found in the fossil record.
B) Because we don't understand how membranes could fold inward to form novel structures within the cell.
C) Because no living cells possess intermediate structures that could tell us how these features originated.
D) All of these choices are correct.