input: The following are multiple choice questions (with answers) about medical knowledge.   **Question:** Phase-contrast microscopy is based on the principle of:   (A) Different refractive indices of object   (B) Different reflective indices of object   (C) Light scattering   (D) Light attenuation
output: ['(A) Different refractive indices of object <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Different refractive indices of object  (B) Different reflective indices of object  (C) Light scattering  (D) Light attenuation <> possible answers', '  Phase-contrast microscopy is based on the principle of: <> context']