Final answer:
Francesco Redi’s experimentation step involved exposing some meat to the air and sealing other meat in containers to test the hypothesis that flies, not rotting meat, produce maggots.
Step-by-step explanation:
Francesco Redi's experiments in the 1600s were a hallmark in the scientific method to disprove the theory of spontaneous generation. The correct option that corresponds with the testing step of the scientific method is 'a.) Redi exposes some meat to the air and places other meat in sealed containers.'
This step directly involves experimentation, which is essential to testing the validity of a hypothesis. Redi's hypothesis stated that rotting meat cannot produce flies; only flies can produce flies. To test this hypothesis, Redi set up different conditions to see where maggots would appear: exposed meat, meat covered with gauze, and meat in sealed jars. The final result was that maggots only formed on the meat that flies could directly access, thus supporting his hypothesis and refuting the theory of spontaneous generation.