input: The following are multiple choice questions (with answers) about medical knowledge.   **Question:** Which of the following is used for selecting patients with respect to potential factors that will affect the results?   (A) Systematic random sampling   (B) Simple random sampling   (C) Stratified random sampling   (D) Cluster sampling
output: ['(C) Stratified random sampling <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Systematic random sampling  (B) Simple random sampling  (C) Stratified random sampling  (D) Cluster sampling <> possible answers', '  Which of the following is used for selecting patients with respect to potential factors that will affect the results? <> context']