Multiple choice

She didn't know where Jo had put the book at.

  1. put the book

  2. left the book at

  3. placed the book at

  4. no change

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Ending a sentence or clause with the preposition "at" in this context is redundant and grammatically incorrect because "where" already establishes the location. Removing "at" to leave "put the book" makes the sentence concise and grammatically correct.