According to the modern concept, cell membrane is

The Fluid mosaic model was developed by Singer and Nicolson in 1972. It is the most widely accepted model relating to cell membranes.

It describes the model as ‘protein icebergs float in the sea of lipids’, which is the quasi fluid nature of the biomembrane.

The lipid bilayer is composed of phospholipids, proteins and sterols which are arranged in different manners in different regions of the membrane.

Hence the correct answer is B i.e, Quasi Fluid