The answer to the question stated above is letter c. Pasteur tested for microorganisms, but Redi studied larger organisms.
Redi experimented with rotting meat; Pasteur experimented with broth. Redi disproved spontaneous generation for large organisms by illustrating that maggots arose from meat only when flies laid eggs in the meat. Pasteur used his famous swan-neck flask experiment, to end the debate. On his experiment air is allowed to contact the broth. Microbes present in the dust were not able to navigate the tortuous bends in the neck of the flask.
