The question whether there is life on Mars   has made the public think a lot for more than a century. The closest look showed Mars to be a dusty, cold world, covered by air too thin to breathe. A British spaceship and Europe's Mars spaceship plan to land on Mars or enter orbit   around it. One of the NASA's   spaceships is expected to land on January 3, the other is going to land on the opposite side of Mars on January 24. Since 1960, over twenty spaceships sent to Mars have failed. Most have been lost on flying up or landing because those are the most difficult times of any flights.     Scientists wanted to find out whether there was water in Mars. In October, a team of scientists reported that Mars had been a dry wasteland. But weeks later, a second team reported differently that they had found some marks showed clearly that they were made by the rivers. Such marks told us that Mars was a warmer place billions of years ago -- just as life first appeared here on Earth. Scientists at once raise a question: if what they said is true, what happened on Mars? Then what about the earth? The most difficult times of a flight are   _  .
taking off flying up and arriving entering the orbit and landing leaving the earth and entering the orbit