Janet's Husband, John, Is Called for Jury Duty and Is

Janet's husband, John, is called for jury duty and is selected for possible service on a jury. However, when he is questioned by the defendant's attorney before final jury selection, he admits that he thinks the defendant is guilty based on the news reports that he saw on the local television news. The defendant asks the judge to excuse John from serving on the jury and the judge agrees. This is:

A) a valid challenge for cause.
B) a valid peremptory challenge.
C) not a valid challenge.
D) a valid challenge, but the plaintiff's attorney can have John serve by making an offer of proof to the judge.