More than a hundred years ago, an American produced   a game. He called it indoor tennis. The Americans were not interested in it at first so he sent it to his London friends and it became very popular   in Britain. The game was then played across the dining-room table or on the floor with the net hung between two chairs. In the early days ,the balls were made of cork   or rubber. The bats  were made of wood. A few years later a hollow   ball like the one we use today was invented. The game then quickly spread all over the world. An Englishman once made a bat covered with rubber. He first played the game in England and called it "ping - pong". "Ping" was the sound of the bat when it hit the ball, and "pong" was the sound of the ball when it hit the table. The name of ping-pong has something to do with   _  .
sound size history place