Final answer:
The first official codification of federal tax laws was the Internal Revenue Code of 1939, which organized existing tax laws into one document. It should not be confused with earlier tax legislation such as the Revenue Act of 1913 or the Internal Revenue Act of 1862, which marked significant developments in the federal tax system.
Step-by-step explanation:
The First Internal Revenue Code
The question asks about the first Internal Revenue Code. While the Internal Revenue Act of 1862 established the Bureau of Internal Revenue and introduced a comprehensive tax measure, the first official codification of federal tax laws was the Internal Revenue Code of 1939. Prior to this, there were important tax legislation, such as the Revenue Act of 1913, that laid the groundwork for the federal income tax system. The Revenue Act of 1942 significantly altered the tax system by lowering the minimum income to pay federal tax. However, it was not until 1939 that these tax laws were codified into what is formally known as the Internal Revenue Code. Therefore, the answer is a. the Internal Revenue Code of 1939.