Which network is NOT part of the "Big Three" US television networks?

The BBC is the correct answer because it stands for the British Broadcasting Corporation, which is a public service broadcaster based in the United Kingdom. While the BBC is a prominent network known internationally, it is not classified as one of the "Big Three" television networks in the United States.

In contrast, NBC, ABC, and CBS are all major American television networks that have played significant roles in the development of the television industry in the U.S. These three networks are known for their extensive programming and have historically dominated the television landscape in America. Therefore, recognizing the distinction between U.S. and U.K. networks helps clarify why the BBC does not belong to the "Big Three" in the context of U.S. television.