1. A synergistic antimicrobial composition comprising: (a) ortho-phenylphenol or an alkali metal salt thereof or an ammonium salt； and (b) 4,4-dimethyloxazolidine； in which the mass ratio of ortho-phenylphenol or its alkali metal salt or ammonium salt and 4,4-dimethyloxazolidine is from 4: 1 to 1: 15.2. The composition according to claim 1, in which the mass ratio is from 3: 1 to 1: 10.3. A synergistic antimicrobial composition comprising: (a) ortho-phenylphenol or an alkali metal salt thereof or an ammonium salt； and (b) tris (hydroxymethyl) nitromethane； in which the mass ratio of ortho-phenylphenol or its alkali metal salt or ammonium salt and tris (hydroxymethyl) nitromethane is from 15: 1 to 1: 15.4. The composition according to claim 3, in which the mass ratio is from 12: 1 to 1: 12.5. The composition according to claim 4, in which the mass ratio is from 10: 1 to 1: 10.6. A synergistic antimicrobial composition comprising: (a) ortho-phenylphenol or an alkali metal salt thereof or an ammonium salt； and (b) hexahydro-1,3,5-tris (2-hydroxyethyl) -s-triazine； in which the mass ratio of ortho-phenylphenol or its alkali metal salt or ammonium salt and hexahydro-1,3,5-tris (2-hydroxyethyl) -s-triazine is from 15: 1 to 1: 15.7. The composition according to claim 6, in which the mass ratio is from 10: 1 to 1: 12.8. The composition according to claim 7, in which the mass ratio is from 9: 1 to 1:10.1. Синергетическая противомикробная композиция, содержащая: (а) орто-фенилфенол или его соль щелочного металла или аммониевую соль； и (б) 4,4-диметилоксазолидин； в которой массовое соотношение орто-фенилфенола или его соли щелочного металла или аммониевой соли и 4,4-диметилоксазолидина составляет от 4:1 до 1:15.2. Композиция по п.1, в которой массовое соотношение составляет от 3:1 до 1:10.3. Синергетическая противомикробная композиция, содержащая: (а) орто-фенилфенол или его соль щелочного металла или аммониевую соль； и (б) трис(гидроксиметил)нитрометан； в которой массовое соо
