用适当的短语完成句子。
hear about, millions of,  try doing sth. go around,
more than, send sb.(a) message(s), try to do sth.?
1. I haven't seen Tom for a long time, so I ______ him ______ .?
2. The earth is a planet and it ______ ______  the sun.?
3. There has been life on earth for ______ years.?
4. There is ______  one galaxy.?
5. They have ______  send information to us.?
6. —Tom, I've just heard that scientists have sent a spacecraft to Mars.?
    —Really?I haven't ______  this yet.

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) ?
    ______________________________________