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 train is called bus, bus is called tractor, tractor is called car, car is called scooter, scooter is called bicycle, bicycle is called moped, which is used to plough a field ?
A 'tractor' is used to plough a field.
But a 'tractor' is called 'car'.
So, a 'car' will be used to plough the field.