Abook review would be considered
a. a primary source.
b. a secondary source.
c. a tertiary source.
d. either a secondary or tertiary source, depending on content.

B. a secondary source.

Explanation:

A secondary source can be define as the source which can be created by someone who write as a review or summery for the first hand document which is generated after research outcome or the original piece of writing.

This source analyzes and interprets the primary source. This source consists of journals, articles, histories, encyclopedias and books.

A book review will be considered in the secondary source as this can be written by the person who is actually not the writer of the book but gives the insight of the notion of the book and it's summary by studying the book.

it is either c or d and i know for sure it is not a or b