In this section, you will hear a short passage. For questions 21—30, complete the notes using no more than three words for each

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问题 In this section, you will hear a short passage. For questions 21—30, complete the notes using no more than three words for each blank. The passage will be read only once. Remember to write the answers on the answer sheet.
-The ocean is still salty.
-Evaporated water leaves【D1】______behind, which makes the ocean salty.
-How did oceans form?
- It is said that oceans formed at least【D2】______ago.
- Atmosphere and clouds on the Earth are gasses, such as【D3】______ escaping from the planet’s interior.
-Were oceans in the past as salty as they are today?
-Oceans were not so salty in【D4】______state.
-With【D5】______ sweeping over the planet’s【D6】______and filtering down to the hollows , materials containing ingredients of salt were picked up.
- Chlorine, came from the【D7】______and gaseous fallout of land and【D8】______volcanoes.
-The oceans’ salt content increases because of the steady flow of【D9】______and streams and the【D10】______of volcanoes and undersea vents.
【D9】
I know why the ocean is still salty: evaporated water leaves the salt behind. But how did it get salty in the first place?
   According to one hypothesis, oceans formed at least 500 million year ago when water vapor and other gasses escaped from the Earth’s interior gradually formed the atmosphere and clouds surrounding the planet. As the earth cooled below the boiling point of water, rain began to fall, and kept falling for centuries. Eventually the rainfall filled the Earth’s hollows and formed oceans.
   In their infant state these oceans were not nearly as salty as they are today. As the initial rains swept over the planet’s surface and filtered down to the hollows, the rushing waters picked up chemicals from erosion of the Earth’s crust. These chemicals included sodium, which is one of the main ingredients of salt. The other main ingredient, chlorine, came from the solid and gaseous fallout of land and ocean floor volcanoes. Over hundreds of millions of years, the steady flow of chemical-rich rivers and streams and the eruption of volcanoes and the undersea vents combined to increase the ocean’s salt content.
   This does not mean, however, that the oceans’ saltiness is constantly increasing. Scientists believe that ocean salinity reached plateau hundreds of millions of years ago, when roughly the same amount of salt fed into the oceans was deposited as sediment on the ocean floor.

选项

答案chemical-rich rivers

解析 (由录音原文“the steady flow of chemical-rich rivers and streams and the eruption of volcanoes and the undersea vents combined to increase the ocean’s salt content”可知,数亿年以来,富含化学物质的河川的稳定流动,以及陆地和海底火山的喷发都促成了海洋盐分的增加。所以此空填写chemical-rich rivers。)
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