The right answer is cell membranes.
A cell necessarily has a membrane, a cytoplasm and genetic information. However, the cells are different: there are prokaryotes, eukaryotes.
A prokaryotic cell is a cell that does not have a delimited nucleus, the genetic information is free in the cytoplasm. For example, the bacteria are prokaryotic cells. Conversely, eukaryotic cells have an envelope-bound core. Inside this one are included the animal and plant cells.