Questions 11 to 13 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions.
Now listen to the passage.
Which of the following is NOT mentioned by the speaker

A．Diamond-producing rivers are located near the mountain sides.
B．Diamonds couldn’t be formed without great heat and pressure of the volcano.
C．Volcano explosions brought some diamonds up to the surface of the earth.
D．Explosions of the volcano can damage diamonds as well.