Answer: Hi!
Your answer would be a), eukaryotic cells. We should automatically know that prokaryotic cells are less complex than eukaryotic cells. However, the last two options, Ebola and Virus, are both viruses. Viruses are not considered living and they don't really do anything besides replicate, which they need living cells to do. On the other hand, Eukaryotic cells have organelles, a nucleus, etc. They are definitely classified as living, and complex!
Hope this helps!
