Final answer:
The testing step of the scientific method corresponds with the activity of experimentation, as observed in Francesco Redi's experiment on flies and meat.
Step-by-step explanation:
The testing step of the scientific method corresponds with the activity of C) Experimentation. In the case of Francesco Redi's observations of flies around hanging meat, his experiment involved setting up containers with different conditions to test his hypothesis. He observed that maggots only appeared on the meat in the open container, supporting his hypothesis that flies were responsible for the generation of maggots. Therefore, Redi's experiment was a crucial step in refuting the theory of spontaneous generation.