I. make up tail-questions: 1.christopher columbus was one of the best-knownexplorers. 2.the age of airplanes changed travel crucially. 3.the age of airplanes made travel available to all people. 4.the cost of air transportation didn't make travel available to eve--rybody. 5.christopher columbus discovered america. 6.amerigo vespucci didn't discover america. 7.afanassy nikitin was not known in the west. 8.the first travellers used simple means of travelling. 9.the first travellers didn't travel by air. 10.they were not familiar with air travel. 11.the trains outdid ships. 12.the trains didn't outdo planes.