A、It can be valid for seven days. B、A yearly pass costs only $18. C、It varies in different seasons. D、It is free for people over

Today we’ll talk about national parks in the United States.
    The United States established its first national park in 1872. Yellowstone, in the western state of Wyoming, is home to grizzly bears, wolves and other animals.
    [23]Yellowstone was not only the first national park in America. It was the first in the world.
    Since then, about 100 nations have followed the example. They have established over 100,000 national parks and protected areas for the enjoyment of people today and generations to come.
    The National Park Service in the United States manages a total of 401 "units," as it calls them.
    These include national parks, historical sites, monuments, buildings and battle fields. They also include recreation areas, seashores, rivers, trails and parkways—almost 34 million hectares of land in all.
    Visitors can hike in the woods. Climb mountains. Photograph animals. Explore Civil War battlefields. Go swimming or river-rafting. Ride horses. Or just enjoy a day outdoors with the beauty of nature.
    The National Park Service was created in 1916. President Woodrow Wilson signed an act to make the National Park Service part of the Interior Department.
    The National Park Service has two main jobs. One is to protect the national parks. The other is to help visitors enjoy them. [24]In 2009, director Ken Bums made a movie about the history of the national parks. He called them "America’s Best Idea."
    One way the National Park Service is able to operate is through the fees it charges. One hundred thirty-three sites charge entrance fees between $5 and $25. [25]Each entrance fee is good for seven days. However, visitors can buy a yearly pass for $80. And people over 62 years old can buy a lifetime pass for $10. A free lifetime pass is offered to people with disabilities.
    In 2012, almost 287 million people visited the American national park system.
    Today the United States has 59 national parks. Wrangell-St. Elias National Park and Preserve is the largest park in the United States. It is in Alaska and covers over five million hectares of land—larger than the size of Switzerland.
23. What do we learn about Yellowstone?
24. What was Ken Burns’ movie about?
25. What do we learn about the entrance fee of national parks?