This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
Soft contact lens is made of ? 
Select and explain. 
A. PMMA, B. HEMA, C. Cellulose acetate butyrate, D. Vinyl monomer
B: HEMA
Answer: B: HEMA 
Explanation: Ans. is 'b' i.e., HEMA Types of contact lenses Depending upon the nature of the material used in their manufacturing, the contact lenses can be divided into three types : - i) Hard lenses : - Made of polymethylmethacrylate (PMMA). ii) Rigid gas permeable (RGP) lenses : - Copolymer of PMMA, silicon containing vinyl monomer and cellulose acetate butyrate (CAB) are used to manufacture RGP lenses. iii) Soft lenses : - These are made up of hydroxymethymethacrylate (HEMA).