根据括号中的要求改写下列句子。
1. He is going to Shanghai. (用现在完成时)
______________________________________
2. I heard about the news about the space travel. (改为同义句)
______________________________________
3. Scientists have found life on other planets.(改为否定句)
______________________________________
4. They haven't been to Mars. (用yet)
______________________________________
5. The spacecraft has reached the moon. (用just)
______________________________________
6. Many astronauts have visited the space station. (用already)
______________________________________
