Final answer:
The example of a eukaryote from the provided options is A) Euglena. Euglenophytes such as Euglena have a nucleus enclosed within a membrane, which is a defining characteristic of eukaryotic cells. The other options are either prokaryotes or viruses, which are not eukaryotes.
Step-by-step explanation:
The example of a eukaryote from the given choices is A) Euglena. Eukaryotes are organisms whose cells have a nucleus enclosed within a membrane, along with various other specialized organelles. Euglenophytes, including Euglena, are unicellular, aquatic organisms that have characteristics of algae and fall under the domain Eukarya, possessing a distinct nucleus. In contrast:
- B) AIDS virus (HIV) is not a eukaryote; it is a virus, which lacks a cell structure and is considered neither a prokaryote nor a eukaryote.
- C) Lactobacillus is a genus of bacteria, so it is a prokaryote.
- D) Cyanobacteria are also prokaryotes as they lack a nucleus and membrane-bound organelles.
Therefore, the correct answer to the question is A) Euglena.