I have been studying to take the CSTE exam in December. I took one of the sample tests of the study guide, and there was a question that I didn't understand the answer and couldn't find it in the study material. On page 6-4, question 8.2 of Test Planning, "What are the two risk levels?", the answers are "LU1 criticality/mission impact" and "LU2 size, system environment, reliability and integration". What is LU1 and LU2, I haven't seen this before and couldn't find any reference in the study guide? Thanks for any help you can provide.