Final answer:
Frederick Griffith demonstrated transformation with two strains of Streptococcus pneumoniae in mice, leading to the discovery of DNA as the hereditary material by Avery, MacLeod, and McCarty.
Step-by-step explanation:
The individual who first demonstrated transformation using mice and two strains of Streptococcus pneumoniae was Frederick Griffith. In 1928, Griffith conducted experiments with two strains of the bacterium: the nonpathogenic rough (R) strain and the pathogenic smooth (S) strain. When he injected live R strain and heat-killed S strain into mice, the mice developed an infection and died, demonstrating that the R strain had been transformed into the S strain. This transformation was mediated by what he coined the "transforming principle." Later, in 1944, Oswald Avery, along with his colleagues Colin MacLeod and Maclyn McCarty, identified the transforming principle as DNA, thereby establishing the role of DNA in heredity.
Avery, MacLeod, and McCarty's experiments advanced our understanding by employing enzymes that degraded each molecular component of the S strain, discovering that only when DNA was destroyed could the bacteria not be transformed, confirming DNA as the hereditary material. Consequently, the correct answer to the student's question is 1) Griffith.