The correct answer is not guilty plea.
A plea is an answer to a claim made by someone in criminal case.
A person accused of a particular crime may plead guilty, not guilty or no contest.
Often, the defendant pleas guilty in order to get more lenient punishment for his crime ( mitigating factor in sentencing). This is called a plea bargain.
A no contest plea is a plea where the defendant submits a plea that neither admits nor denies the offence.