A、For pleasure and excitement. B、For new places where their herds could feed. C、For animals. D、For tree trunks. A信息明示题。根据短文第四段第一

Men have traveled ever since they first appeared on the earth.
   In primitive times they did not travel for pleasure but to find new places where their herds could feed, or to escape from hostile neighbors, or to find more favorable climates. They traveled on foot. Their journeys were long, tiring, and often dangerous. They protected themselves with simple weapons, such as wooden sticks or stones, clubs, and by lighting fires at night and, above all, by keeping together.
   Being intelligent and creative, they soon discovered easier ways of traveling. They rode on the back of their domesticated animals: they hollowed out tree trunks and, by using bits of wood as paddles, were able to travel across water.
   Later they traveled, not for necessity, but for the joy and excitement of seeing and experiencing new things. This is still the main reason why we travel today.
   Traveling, of course, has now become a highly organized business. There are cars and splendid roads, express trains, huge ships and jet airliners, all of which provide us with comforts and security. This sounds wonderful. But there are difficulties. If you want to go abroad, you need a passport and a visa, tickets, luggage, and a hundred and one other things. If you lose any of them, your journey may be ruined.
   Questions 19 to 21 are based on the passage you have just heard.
   19. How were the primitive men’s journeys?
   20. What did they travel for later?
   21. What modern means of transportation are mentioned in the passage?