No one is quite sure how eukaryotic cells first appeared on Earth. Three hypotheses have been proposed for ongoing study. the eukaryote-first hypothesis, the nucleus-first hypothesis, and
A. a hypothesis that begins with mitochondria developing in a prokaryotic cell that later acquired a nucleus
B. a hypothesis that begins with mitochondria changing into a nucleus in a prokaryotic cell
C. a hypothesis that begins with mitochondria developing in a eukaryotic cell that later lost its nucleus