which cell structure is made of a bilayer of phospholipids and encloses all cells?\na cell wall\nb cell…

Brief Explanations:

The cell membrane is a phospholipid - bilayer structure that encloses all cells, regulating the movement of substances in and out of the cell. Cell walls are mainly found in plant, fungal, and some bacterial cells, not in all cells. The cytoskeleton provides structural support and is not a phospholipid - bilayer enclosing cells. Cytoplasm is the gel - like substance inside the cell, not an enclosing structure made of a phospholipid bilayer.

Answer:

B. cell membrane