Which answer choice represents the MOST useful resource for Hilaire in the following vignette?

If Hilarie's vocabulary needs a boost, he needs a thesaurus, which provides a range of synonyms (or antonyms) for words. A dictionary is useful for word meanings, but it will not necessarily assist Hilarie in improving the words he already has in his papers. The encyclopedia is also irrelevant, particularly since the professor already approves of Hilarie's work and is not asking him to research further. The style guide will be helpful if the paper needs more attention on grammar.