Biologists suspect that endosymbiosis gave rise to mitochondria before plastids partly because
a. mitochondrial proteins are synthesized on cytosolic ribosomes, whereas plastids utilize their own ribosomes.
b. mitochondrial dna is less similar to prokaryotic dna than is plastid dna.
c. the products of photosynthesis could not be metabolized without mitochondrial enzymes.
d. all eukaryotes have mitochondria (or their remnants), whereas many eukaryotes do not have plastids.
e. without mitochondrial co2 production, photosynthesis could not occur.