The correct answer is B) They protect justices from political pressure.
The reason why Supreme Court justices are given lifetime appointments was to ensure that they did not have to face an election. If the justices were elected by citizens, they would most likely cater to the demands of citizens when ruling on important cases rather than focusing on interepreting the constitution in an accurate manner. This lifetime membership ensures that they can make judgements in court cases based on the law rather than focusing on how the decision will be viewed by the citizens.