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 eraser is called box, box is called pencil, pencil is called sharpener and sharpener is called bag, what will a child write with ?
The child will write with a 'pencil' and 'pencil' is called 'sharpener'.
So the child will write with a 'sharpener'.