His book has a short but useful introduction.

The correct answer is A. deduction.

An introduction is the beginning of a book, article, or other piece of writing. It is typically used to introduce the topic of the work, provide background information, and state the thesis or main argument. A deduction is a logical argument in which a conclusion is drawn from a set of premises. In the context of the question, the word “deduction” is most likely being used to refer to the introduction of the book. The introduction is a short but useful part