Men have traveled ever since they flint appeared on earth. In primitive times they did not travel for pleasure but to【C1】______new places where their herds could feed, or to escape from【C2】______neighbors, or to find more【C3】______climates. They traveled on foot. Their【C4】______were long, tiring and often dangerous. They protected themselves with simple【C5】______such as wooden sticks or stone clubs, and by lighting fires at night and,【C6】______all, by keeping together. Being intelligent and creative, they soon【C7】______easier ways of traveling. They【C8】______on the backs of their domestic animals they hollowed out tree【C9】______and, by using bits of wood as paddles, were able to travel【C10】______water. Later they traveled, not from necessity, but【C11】______the joy and excitement of seeing and experiencing new things, which is still the main【C12】______why we travel today. Traveling, of course, has now become【C13】______organized business. There are cars and splendid roads, express train, huge ships and jet airliners, all of【C14】______provide us with comforts and security. This sounds wonderful.【C15】______there are difficulties. If you want to go【C16】______, you need a passport and visa, tickets, luggage, nd a hundred and one【C17】______things. If you lose any of them, our journey may be【C18】______. Scientists have invented machines that can explore【C19】______space. Eventually there will be cheap day journey to the moon and honeymoons on Venus. People will be able to fly from one planet to another in nasty little arrow-shaped tubes. I say 'people' because I have no【C20】______of being one of them. 【C1】