Which of the following is NOT an observation about critical​ values? Choose the correct answer below. A. The number Za/2 is a critical value that is a z score with the property that it separates an area of a/2 in the right tail of the standard normal distribution. B. The number Za/2 is a critical value that corresponds to an area of 1-a/2 to its left. C. A critical value is the number on the borderline separating sample statistics that are likely to occur from those that are unlikely to occur. D. A critical value is the area in the​ right-tail region of the standard normal curve.