Astronauts, people who fly into space, need special training. First they go to Houston, Texas. That is the home of the Johnson Space Centre. There they are tested to see how strong and smart they are. One of the first tests is for the heart. The people walk or run, then the space doctors see how fast their hearts are beating. Another important test is performed. In this test the person must curl his body up in a ball. When he is in that position, he is put into a round cloth bag. The doctors give him no idea how long he will have to stay in the bag. If a spaceship broke down in space, the astronauts would get into bags like this. Then they would have to wait and curl up in darkness, until help could arrive. You can see that an astronaut must not be afraid of tight space or darkness. After the tests, only the best people are chosen to start astronaut training in a training centre. The astronauts in training learn many other things. They learn how to jump out of a moving airplane. They learn to how to blow up a lifeboat and get into it while they are in the ocean. The astronauts also have to learn how to get lifted out of the ocean by helicopter . That may look fun, but it can be dangerous. After they finish training, the astronauts continue to work. They stay in good shape by running and doing exercise. They read about their special jobs. In that way they can learn new facts about space travel. Then the big day comes. The astronaut is told to go to work on a flight into space. The crew members get to know each other first. Then they can learn which job each will do. The astronauts don't know how long they will stay in the bag in the test because   _  .
the doctors need to know how strong they are the astronauts need to show how smart they are good astronauts mustn't be afraid of darkness or tight space nobody knows when help will come if the spaceship breaks down