The following are multiple choice questions (with answers) about medical knowledge.   **Question:** According to the instrument formula given by G.V. Black, the primary cutting edge angle should be:   (A) >50 degree   (B) >90 degree   (C) <50 degree   (D) <90 degree
['(A) >50 degree <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) >50 degree \n (B) >90 degree \n (C) <50 degree \n (D) <90 degree <> possible answers', '  According to the instrument formula given by G.V. Black, the primary cutting edge angle should be: <> context@']