I would not diagram this passage if I were taking the exam, but for the purposes of explanation we can break it down as follows:
P: An action's end is its intended outcome. P: The end's value is the only reason for the action. P: Not every ends value will justify any means. P: Perhaps there is no end whose value will justify every means. C: Nothing will justify a means except an end's value.
The key here is not to get caught up in the confusing language used in the passage. The explanation beneath answer choice (C) does a good job of detailing how to break apart the wording of the last sentence in order to identify the conclusion, so I would recommend reviewing that if you haven't already.
Hope that helps! Please let us know if you have any other questions.
