Frederic griffith discovered transformation in his experiments on mice and pneumococcus bacteria. he injected the mice with combinations of harmless, r-strain bacteria and disease-causing s-strain bacteria. which combination of bacteria killed the mice and showed that transformation occurred? a. heat-killed r-strain and live s-strain b. heat-killed s-strain and live r-strain c. heat-killed bacteria of both strains d. live bacteria of both strains