In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.

Question: What characteristic is not common in biological membranes ?:
Options: <1> They are fluid. <2> They are composed of lipids and proteins. <3> They are asymmetrical. <4> They are electrically polarized. <5> The various components are assembled covalently.
5