Exercise ■1 Explain the following words。 Hfr strains: F factors: Photoreactivation: tautomers of base 2. How is the dna in bacteria repaired? 3. What functions do the plasmids have in bacteria?Exercise ◼ 1. Explain the following words。 ◼ Hfr strains； F’ factors； Photoreactivation；tautomers of base。 ◼ 2. How is the DNA in bacteria repaired? ◼ 3. What functions do the plasmids have in bacteria ?