Here's why:

* Eukaryotes are organisms whose cells have a true nucleus, which contains the cell's genetic material (DNA). This nucleus is surrounded by a membrane.

* Prokaryotes, on the other hand, are organisms whose cells lack a nucleus and other membrane-bound organelles. Their DNA is located in a region called the nucleoid, but it's not enclosed by a membrane.

So, all cells with nuclei are eukaryotic cells.