Go back to the text and re-read a passage where Watson made a discovery. If Sherlock praises him, you've got your answer. I'm sorry if this wasn't much help, but I don't have any text to go off of.
Answer:
C)metaphor
Explanation:
Metaphor - A figure of speech that describes a subject by asserting that it is, on some point of comparison, the same as another otherwise unrelated object.
Hyperbole - Exaggerating statements or claims that are not to be taken literally.
Personification - The attribution of a personal nature or human characteristics to something nonhuman, or the representation of an abstract quality in human form.
Alliteration - The occurrence of the same letter or sound at the beginning of adjacent or closely connected words.