It is hard for me to understand the relationship between yields on bonds and how those are related. Can I get a quick little overview on what to look for during a test and how I can make sure i'm answering the question correctly?

ex:

Suppose that the U.S government enacts an across-the-board decrease in income tax rates. Everything else held constant, this would cause the yields on U.S Treasury bonds to________ and the yields on municipal bonds to________. A. increase; decrease B. decrease; decrease C. decrease; increase D. increase; increase