Final answer:
Tax journals are an example of secondary authority, as they offer interpretive analysis and secondary opinions on primary legal documents such as the U.S. Constitution, tax treaties, and tax laws enacted by Congress.
Step-by-step explanation:
An example of secondary authority in the context of law is a source that provides an interpretive analysis, secondary opinion, or a secondhand account as opposed to officially sanctioned legal texts. When considering the options provided, tax journals represent an example of secondary authority. Primary legal sources include official documents such as the U.S. Constitution, tax treaties, and legislation (tax laws) enacted by Congress. Secondary sources, like tax journals, analyze, comment on, and discuss these primary sources, often providing valuable insight but without the binding legal authority of primary sources.