We wondered who/whom the book was about. [a] [b]

Answer 1

In the given sentence, "who" and "whom" can both be used, depending on the intended meaning.

- If the question is referring to the subject, you would use "who":
"We wondered who the book was about." (e.g., Who is the book about? The subject of the book.)

- If the question is referring to the object, you would use "whom":
"We wondered whom the book was about." (e.g., Whom is the book about? The object of the book.)

It's important to note that in many cases, the use of "whom" has become less common in informal speech, and "who" is increasingly used as a universal pronoun for both subject and object.