The Fundamental Idea Behind Challenges for Cause Is That

The fundamental idea behind challenges for cause is that:

A) some jurors will not be able to render an impartial verdict based only on evidence and law.
B) some judges cannot be trusted to conduct jury selection because they may be biased.
C) most jurors should be allowed to challenge witnesses' statements to determine their truthfulness.
D) most judges should not be allowed to question potential jurors because they may taint the jury pool.