In response to my friend's request, I decided to write her a letter, which I hoped would be honest and practical, while also serving as a _________ of sorts for my own feminist thinking. This book is a ______ of that letter, with some details changed.

The sentence explains the author's intention to write a letter in response to a friend's request— one that is honest, practical, and also serves a deeper purpose: it expresses the author's feminist ideas. The second section explains that, albeit with some modifications, a book has been written based on that letter.

A word that explains the purpose or role of the letter is needed in the first blank; it should probably imply that it was a tool, a reflection, or an investigation of the author's thoughts.
A word that expresses that the book is a product, adaptation, or synopsis of that letter is required for the second blank.

We now assess each choice and determine which one best suits our needs.

A. "map, version" — Although the word "map" can figuratively suggest an organised arrangement or strategy, it is a little awkward when used to convey introspective thoughts about one's own ideology. "Version" is a good second word because it accurately describes a modified or reworked form. All things considered, this is not the best fit but is partially accurate.

B. "chart, form" — "chart" is even more technical than "map" and isn't appropriate for the letter's reflective, personal tone. In this context, "form" is ambiguous and lacks the precision of "version" or "precis." The words are therefore not a suitable fit.

C. "base, fallout" — "base" might imply a foundation, which is somewhat appropriate for the first blank, but "fallout" is completely inappropriate here because it is highly negative and suggests consequences or damage. (incorrect meaning and tone.)

D. "guide, precis" — Using "Guide" in the first blank implies that the letter functioned as a thoughtful framework or reflection of the author's feminist thinking, which is a perfect fit for the first blank. "Precis" fits the second blank perfectly because it refers to a concise summary or abstract, which is what a book based on that original letter would be described as. The tone, meaning, and intent of both words are all in harmony.

Option D is therefore the correct answer in this case.