Common law (also called case law or precedent) is a source of law that is derived from:

a. a single document that contains all laws.
b. court decisions.
c. popular culture.
d. federal rules and regulations.

The answer is B. Court decisions.

Explanation:

Common law refers to a law that is derived from courts' judicial decisions as well as other similar tribunals. The most important characteristic of common law is that it emerges as a precedent.

Common law is usually utilized when the parties disagree about the establishment of a specific law. In this case, a common-law court reviews the decisions that were considered in the past by relevant courts and summarizes the different principles related to those cases to apply them to the current facts.  

by using  production possibilities graph.  opportunity costs are key expenses in financial matters and are utilized as a part of registering money saving advantage investigation of a venture. such expenses, be that as it may, are not recorded in the record books but rather are perceived in basic leadership by processing the money costs and their subsequent benefit or misfortune.