In substitution type of questions, some particular objects are assigned code names. Then a question is asked that is to be answered in the code language.
If book is called watch, watch is called bag, bag is called dictionary and dictionary is called window, which is used to carry the books ?
Clearly, a 'bag' is used to carry the books but a 'bag' is called 'dictionary'.
So, a 'dictionary' will be used to carry the books.