阿基米德说：给我一个支点，我能撬动整个地球。这句话精辟的阐明了他在物理学上的一大贡献是（    ）

   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. 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.

如图所示的家用电器中主要是将电能转化为内能的是（　　）