According to the Lamellar or Sandwich models, cell membranes contain both protein and lipids in distinct layers. Two such models were popular Danielli and Davson model and Robertson's model. Robertson gave unit membrane concept which proposed that all biomembranes have a trilaminar structure. According to Danielli and Davidson, 1935, plasmalemma is a double phospholipid layer surrounded on either side by a layer of hydrated globular proteins in the form of "Protein-Lipid-Lipid-Protein". The hydrophobic or non-polar tails of the two lipid layers are towards the centre. Thus, the correct answer is option A.