Riddle: There was a man who had lots of money, he was very rich. The man had 3 sons. The man knew that he was old and was going to die very soon. He wanted his money to go to his wisest son. So he gave them some money and showed them a room. He said"Buy me something that can fill this whole room and I will give you all my money. The first son bought heaps and heaps of straw but the man said that there were still holes with the straw. The second son bought many grains of sand. But how much he seemed to buy, was always not enough. The third son bought something that filled the whole and he got all his father's money. What did the third son buy?
Answer: The third son bought a candle that filled the whole room up with light.