what is the main reason that federal judges are appointed to their position for life rather that a specific term like most politicians?

A) Because many cases take years and years to review.
B) So, they will make decision based on what they think is right, rather that on what they think will help them keep their job.
C) In order to allow the to learn their job and become good at it over time.
D) Because most of them are old and will retire soon away.