1. Before I read articles about Pham Tuan, I had learnt about him.
2. Around 8,378 atellites have been sent to space since the launch of Sputnik 1 in 1957.
3. Do you know the reason why many people around the world learn English?
4. Ann said that she had gone to the National Air and Space Museum with her friends the day before.
5. If Martin were a U.S. citizen, he could apply for NASA astronaut training. 
6. Men haven't gone to the Moon for a long time.

7. As a result of the earthquake, many roads in the area have been closed.
8. Most parents would rather their children studied a useful subject leading to a good job.
9. If you press that button on the keyboard, you'll lose what you've written.
10. Jim asked his father how long it took to get to Mars.