Choose the most suitable option to replace the highlighted part of the sentence: He did not know where was the book kept.

Correct — A. where was the book kept is an embedded question: it sits inside the statement He did not know, as the object of know.

Embedded questions take statement order, subject before verb:
where the book was kept

The passive was kept also stays whole, since someone kept the book. That is option (a).

Why the others are wrong

• (b)
  where was the book — where was the book keeps the question order and drops kept, so it asks where the book was, a different meaning, and is still inverted.
• (c)
  where did the book kept — did the book kept pairs did with the past form kept, where did needs the base verb. It keeps question order and makes the book the keeper.
• (d)
  where the book has kept — the book has kept has the right order but the wrong voice: the book becomes the keeper. Its present perfect also clashes with the past did not know.

A question inside a statement loses its question order. Where was the book kept? is a direct question, auxiliary before subject. After He did not know, it becomes a noun clause, and the subject returns to the front: where the book was kept.

The same holds after ask, wonder and do you know: Do you know where she lives? The question mark there belongs to the main clause.

Key facts

• Embedded questions use statement order: I wonder where he is, not where is he.
• Did, do and does take the base form of the verb: did keep, never did kept.
• An embedded question after a statement ends with a full stop, not a question mark.

Common traps

• Keeping the inversion because the clause begins with the question word where.
• Choosing has kept for its correct word order without noticing it turns the book into the keeper.

No directly related past PYQ was found.