A small selection of terms was found at the back of the textbook. It was a A. Glossary B. Preface C. Diction D. Kefir E. Prefece

I would say that the answer to the question would be A.
Glossary.  The glossary feature of a work traditionally appears at the end of a book and
contains terms or vocabulary that has been featured or discussed in the work.  It is a
reference tool that allows for a quick cross check of items in the
work.

The other options are not necessarily best equipped
to answer the question.  Diction, in this case, would be short for "dictionary" and that
would be another reference work, standing entirely on its own.  The Preface is something
that appears at the start of a work.  The other options simply do not contain the same
information or meet the standard best as the term, "Glossary," does.  With this in mind,
I would think that "Glossary" best answers the question.