Answer:
See the answer below
Step-by-step explanation:
If Pasteur had tilted one of the flasks so that sterile broth entered the swan neck and then tilted it back to allow the broth to settle back, that particular flask would have had microbes growing in it after being left undisturbed for a few days.
Allowing the sterile broth to get to the neck of the swan would lead to the contamination of the broth because the swan neck is not sterile. If this had happened, the observation of growth of microbes in one of the flasks would have given further credence to spontaneous generation.