| Adrenaline | John Jacob Abel | U.S. | 1897 |
| Aerosol can | Erik Rotheim | Norway | 1926 |
| Air brake | George Westinghouse | U.S. | 1868 |
| Air conditioning | Willis Carrier | U.S. | 1911 |
| Anesthetic | Crawford W. Long | U.S. | 1842 |
| Antiseptic | Joseph Lister | England | 1867 |
| Antitoxin | Emil von Behring | Germany | 1890 |
| Aspirin | Dr. Felix Hoffman | Germany | 1899 |
| Atom | Ernest Rutherford | England | 1911 |
Good one
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