A. The hosts body could reject the transplanted stem cells
This is the chronicle of evolution over millions of years of geologic time engraved in the order which fossils appear in rock strata.
Mmm idk why either. Evolution is not proven as no one kept apes and see it grow into a human. It doesn't really make sense too. Animals don't have moral judgement, and can't create and understand images of art and drawing. It is weird if apes somehow adopts the abilities and become a human.
Also viruses have nucleic acid whether DNA or RNA nucleic acid, they are so minute that you can't observed them,
it's letter C, they are also responsible for proteins. their cell wall is made up of capsid.