Which government body administers tax collection and enforcement in the U.S.?

The Internal Revenue Service (IRS) is the correct answer because it is specifically designated as the federal agency responsible for administering and enforcing the internal revenue laws of the United States. This includes overseeing the collection of federal taxes, processing tax returns, issuing refunds, and ensuring compliance with tax regulations. The IRS plays a crucial role in the government's ability to fund its operations and services through tax revenue.

The Department of Treasury does oversee the IRS and is involved in broader economic policy and managing government revenue, but it is the IRS that directly handles tax collection and enforcement. The Federal Bureau of Investigation (FBI) focuses on national security and law enforcement, while the Census Bureau is concerned with population and demographic data rather than tax-related matters, which clarifies why they do not fulfill the role assigned to the IRS.