Once there was a crow . It was very thirsty .It flew in search of water but found no water .At last,it was a jug of water in the garden. It reached to the jug but water was very low . It couldn't drink it. It looked here and there and saw few pebbles nearby. It thought of a plan. It but pebbles into the jug. The water rose up. It drink water and flew away.
MORAL:-
Necessity is the mother of invention.