Question 9 is based on the passage you have just heard.

Passage One

听力原文

     While some scientists explore the surface of Antarctica, others are learning more about a giant body of water four kilometers beneath the ice pack. (9) [Scientists first discovered Lake Vostok in the 1970s by using radio waves that penetrate the ice.] Since then, they have used sound waves and even satellites to map this massive body of water.

    How does the water in Lake Vostok remain liquid beneath an ice sheet? “The thick glacier above acts like an insulating blanket and keeps the water from freezing,” says Martin Siegert, a glaciologist from the University of Wales. In addition, geothermal heat from deep within the earth may warm the hidden lake. (10) [The scientists suspect that micro-organisms may be living in Lake Vostok, closed off from the outside world for more than 2 million years.] “Anything found there will be totally alien to what’s on the surface of the earth,” says Siegert. 

    Scientists are trying to find a way to drill into the ice and draw water samples without causing contamination. Again, robots might be the solution. If all goes as planned, a drill-shaped robot will melt through the surface ice. When it reaches the lake, it will release another robot that can swim in the lake, take pictures, and look for signs of life. (11) [The scientists hope their discoveries will shed light on life in outer space, which might exist in similar dark and airless conditions.]

    Recently, close-up pictures of Jupiter’s moon, Europa, shows signs of water beneath its icy surface. Once tested in Antarctica, robots could be sent to Europa to search for life there too.

9. What did scientists first use to discover Lake Vostok in the 1970s?

解析：A。录音开头在讲到沃斯托克湖时，提到了两个与时间有关的词，一个是in the 1970s，另一个是Since then。根据录音内容，在20世纪70年代，科学家们通过无线电波（radio waves）发现了沃斯托克湖，此后又利用声波（sound waves）和卫星（satellites）来绘制这片水域。因此A项为正确答案。

错项排除：B项和D项的干扰性较强，但时间点对应错误，声波和卫星是在发现沃斯托克湖之后才使用的，故排除。录音随后又提到，科学家想利用机器人（robots）来提取沃斯托克湖的水样，但那是未来可能的研究计划，故C项排除。解题的关键在于听准时间点和各种工具的对应关系。