A、Under the river bed. B、On the floor of the sea. C、In the volcanoes. D、At the foot of the mountains. C细节辨认题。文中指出It is in the na

The diamond is considered the most famous and valuable jewel in the world. A diamond is a symbol of wealth. Diamonds were made as a result of great volcanic heat and pressure. A volcano is a mountain with a hole on the top. A volcano can be very dangerous because when it is active it sometimes explodes and causes great damage. Diamonds were pushed towards the surface of the earth—millions of years ago by a number of great volcanic explosions. It is in the narrow volcanic pipes that diamonds are found. They are also found among the sand and stones of certain river beds, and in a few places on the floor of the sea for they were washed down the mountain sides by the rain.
   Diamonds are very rare. There are not many diamond pipes or diamond-producing rivers in the world. During the last century adventurers from Europe went to Brazil, because they had heard that there were diamonds in the River Amazon. Many of these early diamond miners died of illness or went lost forever in the great forests. But some re turned home rich.
   The earliest known diamonds were found in India many centuries ago. The most recent and exciting discoveries have been made in eastern Russia. But most of the world’s diamonds now come from Congo, from Tanzania—which has the largest diamond mine in the world—and from South Africa.
   Questions 19 to 21 are based on the passage you have just heard.
   19. What can we learn from the passage?
   20. Where did diamonds first come into existence?
   21. What do you think is the best title for the passage?