Most eukaryotic cells contain mitochondria, but a few single-celled eukaryotic organisms found in oxygen-free environments do not

Question

Which of the following observations led biologists
to reject the hypothesis that these mitochondria-free eukaryotes evolved BEFORE the
endosymbiotic event that established mitochondria in other eukaryotes?
A. All eukaryotes exhibit some sort of energy
utilization.
B. Some eukaryotes don't have mitochondria,
they have chloroplasts instead.
C. The nuclear genome of these mitochondria
-free eukaryotes contains relics of
mitochondrial genes.
D. All eukaryotes have remnant chloroplast
genes.

Answer 1

C