Final answer:
Elizabeth Johnson Jr. was unable to be exonerated for over 300 years due to being falsely accused, insufficient evidence, and potential bias in the legal system.
Step-by-step explanation:
Elizabeth Johnson Jr. was unable to be exonerated for over 300 years because of a combination of reasons. First, she was falsely accused of a crime, which led to her wrongful conviction. Second, there was insufficient evidence at the time to prove her innocence. Lastly, the legal system during that period may have been biased, which hindered her chances of being exonerated.