Us tax court is part of which one of the following levels of federal courts?

There are three levels of federal courts in America, and those are: district/trial courts, circuit courts, and the Supreme Court.
Using the system of elimination, we can rule out the Supreme Court immediately. Circuit courts are the second level of appeals, which taxes don't belong to, so this option is also incorrect. This leaves us with district courts. 
US Tax Court is part of the district/trial courts.