Mark the letter A, B, C, or D on your answer sheet to indicate the correct option that best fits each of the numbered blanks 

Living in the mountains can be very hard. First, there is  _______ to grow crops or raise livestock. _______ houses is also difficult because the land is not flat. The air in the mountains is  _______. The higher we get, the thinner the air becomes. This means there is less oxygen, which makes breathing harder.

Despite these challenges, people around the world have lived and worked in mountainous areas for centuries. There are many health benefits of living in the mountains. Being on the mountaintops  _______ you to live far from pollution. The air you breathe is fresher. There are places where you cannot drive a car or a motorbike,  _______ you have to walk. Travelling up and down hills and mountains on foot helps keep  _______. Finally, mountain people are quite simple and friendly. They live a peaceful life.