The most important mechanism by which tetracycline antibiotics exert antiimicrobial action is (a) They chelate Ca2+ ions and alter permeability of bacterial cell membrane (b) They bind to 30S ribosomes and inhibit bacterial protein synthesis (c) They bind to 50S ribosomes and interfere with translocation of the growing peptide chain in the bacteria (d) They interfere with DNA mediated RNA synthesis in bacteria