Hello.
The correct answer is "A.) Thesaurus". This is because Thesauruses contain most or all synonyms and antonyms, while dictionaries contain primarily just definitions and pronunciation. Encyclopedias are Internet-based sources that contain videos, images, and other information, but do not contain synonyms.
A glossary is essentially a very brief dictionary; it contains terms and definitions, reference pages, and all the sorts. But they do not contain synonyms.
I hope this helps!
The correct answer is A. reliable.
The writer was 'an authoritative source' because of her degrees, guest appearances, etc. Thus, she was a source you could rely on, she was reliable, given that she had experience to back her ideas up. Therefore A is the only correct answer.