The following are multiple choice questions (with answers) about medical knowledge.   **Question:** Which focal length in the objective piece of microscope is commonly used for ear surgery?   (A) 100mm   (B) 250 mm   (C) 450mm   (D) 950 mm
['(B) 250 mm <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) 100mm \n (B) 250 mm \n (C) 450mm \n (D) 950 mm <> possible answers', '  Which focal length in the objective piece of microscope is commonly used for ear surgery? <> context@']