What explains the death of the experimental mouse injected with heat-killed lethal S strain and nonlethal R strain?

• A. The S-strain bacteria became active upon exposure to other bacterial strains.
• B. Hybrid strains were formed from the two bacterial strains.
• C. The heat-killed S-strain released toxins that killed the mouse.
• D. The R-strain took up the DNA from the lethal heat-killed S-strain.

Answer: (D)