John Needham performed a series of experiments based on Redi's experiment to support the theory of spontaneous generation. In his experiment, Needham boiled different kinds of broth in flasks, sealed them, and then let the broth cool. Microorganisms developed in the broth, providing Needham with evidence of spontaneous generation. Even though Needham's results supported the theory, what criticism did other scientists have about the experiment? A. The experiments were conducted only once.
B. Sterile flasks should have been used in the experiments.
C. The broth was contaminated before the flasks were sealed.
D. A greater variety of broth should have been tested.