The specific part of moving from second to the third level that stood in the way of Keith Nolan is:
This refers to the use of obstacles or hurdles to check whether a person is fit to go to the next level or it can also come as a form of assessing the mental or physical ability of a person.
With this in mind and from the complete question, we can see that Keith Nolan is undergoing a ROTC training and the specific part where he was to pass to get to the third level was the hearing test.
Read more about tests here:
https://brainly.com/question/24863377