The following are multiple choice questions (with answers) about medical knowledge.   **Question:** A study was done where the sale of anti-asthma drug was recorded and the number of deaths because of asthma was measured over a period of 15 years (1975-1990). This is which type of study.   (A) Ecological   (B) Case reference   (C) Experimental   (D) Psephology
['(A) Ecological <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Ecological \n (B) Case reference \n (C) Experimental \n (D) Psephology <> possible answers', '  A study was done where the sale of anti-asthma drug was recorded and the number of deaths because of asthma was measured over a period of 15 years (1975-1990). This is which type of study. <> context@']