Which of the following is not a valid Red Book rating A A1 B

Which of the following is not a valid Red Book rating?

A. A1

B. B2

C. C1

D. C2

Solution

A. The Red Book lists the following ratings: B2 Good, C2 Fair, C1 Minimum, and None. Therefore, answers B, C, and D are incorrect because the question asked what is not a valid rating.