TOPIC: Procurement risk contradiction (head first vs RITA)

In Head First book,a question as follows

Which of the following contracts has the MOST risk for the buyer?
A. Cost plus fixed fee (CPFF)
B. Time and materials (T&M)
C. Cost plus award fee (CPAF)
D. Fixed price (FP)

Ans is B

But according to RITA, the T&M risk is just medium , C is the answer.....

I think I believe RITA is better for this case?

Any idea?

See this thread: www.project-management-prepcast.com/kune...-buyer-the-most-risk