Answer: The correct answer is B) Membrane.
A cell membrane is present around the cytoplasm of all cells. It is a protective, selectively permeable membrane of the cells that regulates the transport of molecules in and outside the cell. It acts like a boundary that separates the cell interior from its external environment and helps in maintaining homeostasis.
On the contrary, nucleus is present in eukaryotes only and cytoplasm is not a boundary rather a fluid compartment of the cell. Cell wall ( around cell membrane) is not present in animals, which are eukaryotes.
Thus, B) Membrane is the right answer.