An encyclopedia is an example of a select one: a. online database b. reference work c. journal d. periodical

B). Reference work.

Explanation:

Reference works are described as a periodical work or book that are primarily intended to provide factual information to the readers and to which they can refer for established/confirmed information or facts. Such works are not meant to be read from the introduction or beginning to the end but rather a compendium intended to make it convenient for reference either in pieces for varied purposes or as a whole.

As per the question, 'encyclopedia' exemplifies a 'reference work' as it is used a compendium to which people refer for information and for ensuring/confirming facts. It(encyclopedia) offers a vast range of subjects and domains along with their varied aspects that propose a flood of information out of which the readers could refer to as per their interests and subjects. Thus, option B is the correct answer.