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
[{'content': 'Rigid gas permeable lens are made of- \nSelect and explain. \nA. Plymethymethacrylate, B. Hydroxymethylmethacrylate, C. Co polymer of PMMA, Silicon containing monomer & cellulose acetyl butyrate, D. Cellulose acetae Butyrate', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 1. Hard lenses: Made of pokymethylmethacrylate (PMMA) 2. Rigid gas permeable (RGP) lenses: Copolymer of PMMA, silicon containing vinyl monomer & cellulose acetate butyrate (CAB) are used to manufacture RGP lenses. 3. Soft lenses: These are made up of hydroxymethymethacrylate (HEMA)', 'role': 'assistant'}]