Answer: A. thesaurus
Step-by-step explanation:
A thesaurus is used to get the synonyms of words. It compiles words that can be used to replace one another.
An almanac is a calendar that contains information regarding statistics like tide tables and astronomical data and also contains important dates. Encyclopedia or encyclopaedia gives information on various subjects.
Based on the above, thesaurus is a useful tool to prevent Sara from accidentally plagiarizing or copying the words that the authors have used.