题目

Have you ever seen people building houses? To build a house , you need workers. They use their hands , tools(工具) and machines to put things together. Building the ISS（国际太空站） is the same. The difference is that the workers are astronauts. They walk in space and use robots’ arms and hands to do their work.In the space station ,astronauts are comfortable. The temperature there is about 21℃.But outside the station , it can be too hot or cold for people. In the sunlight, it’s about 120℃. In the shadow(阴暗处)of the station, it’s about -85℃ . So when astronauts walk “0”不能做被除数．________．