根据短文理解选择正确答案。

      A long time ago, the monkey and the turtle were good friends. One day, they saw a fallen banana tree and decided to plant it. They divided the tree into two parts. The monkey took the part with leaves, thinking that it would grow faster, then they went home and planted it. Many days passed, the monkeys plant died but the turtle's grew well and produced fruit. When the fruit was ripe(成熟的) the turtle asked the monkey to share it with him. The monkey climbed up the tree and ate all the fruit. So the turtle got angry. He found some sharp sticks and put them around the tree. When the monkey came down, he hurt himself. The turtle laughed and hid himself under a big shell (贝壳). The monkey got very angry and caught the turtle.

  “I'll cut you into pieces,” said the monkey.

  “Good, so there will be many turtles.”

  “No, I'll put you into the fire.”

  “That's better, my skin will be red.”

  “No, I'll throw you into the river.”

  “No,” said the turtle, “I'll die.”

    The monkey threw the turtle into the river, and the turtle swam happily.

振动越快，发出的声音就越高。（    ）