It's late evening in the middle of the winter． The snow is deep， but off I go into the wild．Suddenly， I hear it： the howl （嚎叫） of wolves． Excitedly， I walk faster in the direction of the howling．

    I've been working as a volunteer wolf tracker in Yellowstone National Park for over a year． It's my job to follow wolves to record information about them． Like wolves， however， I don't work alone． I'm one of a team of people who have been in a project to help reintroduce wolves to the park．

    Humans have always feared wolves． From fairy tales to movies， the wolf is always the bad guy a danger to humans and other animals． In the 1920s， the organizers of the park shared this view about wolves and made the decision to drive them away from the park．As a result，the number of elk（麋鹿）in the park increased． The elk started looking for food near river banks since they didn't have to worry about wolves．This， in turn， stopped trees from growing along the rivers， doing great harm to the environment there．

    The return of wolves has already made a big difference． To begin with， the elk soon learned to stay away from the rivers， so new trees have been able to grow there． The trees become home to new wildlife， such as birds， and provide food for more animals．

    The park is now becoming more and more popular with those who want to see wolves in their natural environment． It has also helped the local people make more money， Tourists visit the area，stay in the local hotels， and eat in the local restaurants．

    Looking at the wild animals and the beautiful sceneries around me， I am amazed at the changes the wolf has made to Yellowstone．And happily，it is playing a good guy in this story．

（1）According to the passage， one of a wolf tracker's jobs is to　　．

A． catch wolves in the park

B． feed wolves in the wild

C． stop wolves from killing elk

D． collect information about wolves

（2）Why did the organizers drive the wolves away from the park in the 1920s？　　

A． The wolves were always howling at night．

B． The elk in the park were in danger of dying out．

C． The wolves had done great harm to the environment．

D． The park was thought to be unsafe with wolves around．

（3）Paragraphs 4 and 5 are mainly about the　　that wolves have brought to Yellowstone．

A． risks

B． troubles

C． changes

D． competitions

（4）What does the writer mean by the underlined sentence in the last paragraph？　　

A． Wolves are important to Yellowstone．

B． Yellowstone has been home to wolves．

C． The wolf and the elk live in peace now．

D．The number of wolves is growing fast．