单项选择题

Tourism(旅游) was not always as important as it is today.
In the past only wealthy(富有的) people could travel (41) vacations to other countries. More people travel today than in the past (42) there is a growing middle class in many parts of the world. People now (43) more money for travel. Special airplane fares for tourists make travel (44) expensive and thus more attractive(有吸引务的) than (45) before.
One person does not travel for the same reason as (46) . But most people enjoy (47) countries that are different from their own. They also like to meet new people, try new food and (48) life in other parts of the world.
Tourism (49) many changes in a country and in people’s lives. People build new hotels and restaurants and train native men and women 50 tour guides to show tourists interesting places.