One thing about the moon many people don’t know is that it has a lot of garbage on its surface, leftover from human space exploration. But how much garbage exactly have humans left on the moon? It’s hard to be accurate, but the trash likely weighs more than 181,000 kilograms on Earth. Much of it was left by American astronauts who landed on the lunar surface between 1969 and 1972 during NASA’s Apollo missions. The other rubbish comes from missions that did not have human crews. These missions were conducted by various space exploring agencies, including those from the US, Russia, Japan, India, and Europe. Many of the older pieces are equipment sent to learn about the moon. The equipment stayed there after its missions ended. The moon is also home to lunar orbiters that mapped the moon before they crashed into its surface, adding to the garbage heap. The objects left by the Apollo astronauts included equipment that was no longer needed. Bringing back unneeded equipment would have used up precious resources such as fuel. But, as the saying goes, one person’s trash is another’s treasure. Researchers can study the garbage left on the moon to see how its materials weathered the radiation and vacuum of space over time. Moreover, some of the objects on the moon are still being used, including a laser-range reflector left by the Apollo 11 crew.
关于月球有一件事很多人不知道，那就是月球表面有很多垃圾，是人类太空探索留下的 。但是人类究竟在月球上留下了多少垃圾呢？这很难准确，但这些垃圾在地球上的重量可能超过18.1万公斤 。1969年至1972年，美国宇航员在执行阿波罗任务期间登陆月球表面，留下了大量的月球垃圾 。这些任务由不同的太空探索机构执行，包括来自美国、俄罗斯、日本、印度和欧洲的机构 。许多时间较长的碎片是用来研究月球的设备 。这些设备在任务结束后留在那里 。月球也是月球轨道飞行器的家园，这些飞行器在撞击月球表面之前就绘制了月球地图，这增加了月球的垃圾 。阿波罗号宇航员留下的物品包括不再需要的设备 。把不需要的设备带回来会耗尽燃料等宝贵资源 。但是，俗话说，一个人的垃圾是另一个人的财富 。研究人员可以研究留在月球上的垃圾，看看月球上的物质是如何经受时间的辐射和真空的 。此外，月球上的一些物体仍在使用，包括阿波罗11号宇航员留下的一个激光反射器 。
Questions 19 to 21 are based on the passage you have just heard.
19.What does the passage say may be unknown to many people?
20.Why has a lot of equipment been left on the moon?
21.What can researchers do with the garbage on the moon?