When thinking about placing a human being in space, one of the most important questions was how to design special clothing needed to protect a person from the dangers of the space environment. The cold of space will freeze skin in a short time. The fierce heat of the sun can cause serious burns. The lack of atmosphere can cause gases in the body to expand  and even burst. With no oxygen to breathe, a human being will die in only a few moments. Radiation from the sun is another risk in space. So is damage from small pieces of rock and objects like meteoroids  . In 1933, an American flyer, Wiley Post, designed one of the first successful devices to protect a pilot at extreme heights. It was a large device that looked like a can surrounded the pilot's head. Astronauts in the American space agency (NASA) flew the first American space flights in the early 1960s. The clothing was similar to that invented by Wiley Post. Today, astronauts wear very different protective clothing. It lets them move, do useful tasks, and stay outside their spacecraft in comfort and safety for several hours. The spacesuit is called the shuttle extravehicular mobility unit or EMU. It was designed to _ longer and to permit more movement than earlier spacesuits. The EMU has a number of parts that an astronaut can link together by using only one hand, which makes it possible for each astronaut to select the parts that fit correctly. Nowadays, NASA scientists are also considering the kind of spacesuits that would be needed for exploration on the planet Mars. Because of the gravity on Mars, spacesuits may have to be designed to be lighter than suits used in orbit or on the moon. The equipment may also have to protect astronauts from dust carried in the winds on Mars. And, they must be easy to repair and keep clean during a longer flight to and from the red planet. The best title of the passage might be   _  .
Space exploration Astronauts' flights The Advantages of Spacesuits The Development of Spacesuits