A precedent is a legal case that establishes what is called "principle or rule." This principle is used by the court when deciding later cases with similar issues or facts. This is because the Courts in the U.S. legal system wish to have consistent rulings in similar cases.
The answer to the question you have presented above would be letter a. To show that other cases with similar circumstances came to a similar decision. Justices use precedents in majority opinions and dissents in order t<span>o show that other cases with similar circumstances came to a similar decision.</span>
