Eukaryotic cells are a type of cells that make up complex organisms like plants, animals, fungi, and protists. These cells are characterized by the presence of a distinct nucleus, which is a membrane-bound organelle that houses the genetic material of the cell. Let's break down the options given and see which ones are correct.

Distinct nucleus:
- The presence of a distinct nucleus is one of the defining features of eukaryotic cells. The nucleus contains the cell's DNA, which carries the instructions for making proteins and controlling cellular activities.

Nucleolus:
- The nucleolus is a substructure within the nucleus. It is responsible for producing ribosomes, which are the cellular structures involved in protein synthesis. The nucleolus is involved in the assembly of ribosomal RNA (rRNA) and ribosomal proteins.

Nuclear membrane:
- The nucleus is surrounded by a double membrane called the nuclear envelope or nuclear membrane. It separates the contents of the nucleus from the rest of the cell and regulates the passage of molecules in and out of the nucleus. The nuclear membrane is made up of two phospholipid bilayers with nuclear pores that allow selective transport of molecules.

Nucleoid:
- The nucleoid is a term used to describe the region in prokaryotic cells where the genetic material is located. Prokaryotic cells, such as bacteria, do not have a distinct nucleus like eukaryotic cells. Instead, their DNA is present in a region called the nucleoid, which is not enclosed by a membrane.

Based on the options given, the correct answer is option (d) - all of these. Eukaryotic cells have a distinct nucleus, a nucleolus within the nucleus, and a nuclear membrane that surrounds the nucleus. The presence of these structures distinguishes eukaryotic cells from prokaryotic cells, which lack a distinct nucleus and other membrane-bound organelles.