Answer:
I believe the detail that best supports the inference is:
D. When he first hears the moor's silence broken, he was exultant.
Step-by-step explanation:
The inference states that Holmes was expecting something to appear on the moor. If he was expecting it, he would probably be happy, excited to hear a noise, since it would be proof that he was right, that something was indeed going to show up. That's why the detail "When he first hears the moor's silence broken, he was exultant" is the best to support such inference. It mentions Holmes's reaction - a reaction that confirms his expectation. Had he not expected anything to appear, he would not have been exultant, but would have been scared or surprised instead.