I was wondering if anyone is familiar w/ any subtle differences between the two? (I did my LR through the Trainer, where the 'justify reasoning' questions are known as 'sufficient assumption', while the 'justify conclusion' ones are known 'supporting principle -- they're in the same chapter, and for both types, you're supposed to "fill in the logical gap").

The question is a "which of the following propositions is best illustrated by the situation described in the passage?"/ a principle one.

I'm not sure as to why (D) is not the correct choice, and why it's (C).