Different citation styles have specific elements that must be included in an audio citation. Typically, books citations include some or all of the following elements.
The 2nd example is an ebook. If the work is not directly available online or must be purchased, use "Available from," rather than "Retrieved from," and point readers to where they can find it. For books available in print form and electronic form, include the publish date in parentheses after the author's name.
Electronic books are cited exactly as their print counterparts with the addition of a media marker at the end of the citation: Kindle edition, PDF e-book, Microsoft Reader e-book, Palm e-book, CD-ROM, etc. Books consulted online are also cited exactly as their print counterparts with the addition of a DOI (or URL) at the end of the citation. Stable page numbers are not always available in electronic formats; therefore, you may, instead, include the number of chapter, section, or other easily recognizable locator.