1. Christopher Columbus was one of the best-known explorers, wasn't he?
2. The age of airplanes changed travel crucially, didn't it?
3. The age of airplanes made travel available to all people, didn't it?
4. The cost of air transportation didn't make travel available to everybody, did it?
5. Christopher Columbus discovered America, didn't he?
6. Amerigo Vespucci didn't discover America, did he?
7. Afanassy Nikitin was not known in the West, was he?
8. The first travellers used simple means of travelling, didn't they?
9. The first travellers didn't travel by air, did they?
10. They were not familiar with air travel, were they?
11. The trains outdid ships, didn't they?
12. The trains didn't outdo planes, did they?
