A、A diary. B、A fairy tale. C、A history textbook. D、A biography. D短文开头提到了《约翰·缪尔传》这本书。接着对这部自传进行了介绍，故D)为答案。

Here’s Biography of John Muir—John Muir’s own writings to bring readers a life story of this remarkable man who did so much to raise the America’s awareness of environmental issues. As America’s first environmentalist, John Muir lived his life for ever daring for undertaking new adventures. He spent most of his days outdoors and had deep love for the wild lands. In the book, we meet John Muir as a youth fearlessly climbing the roof of his house. He captures birds only to let them go when he realizes the cruelty involved. He becomes an inventor and sells his inventions in order to attend the university. As a young man, he began walking over tens of thousands of miles during his lifetime, through the south to Florida, the west to California and north to Alaska, where readers are taken a long and particularly hair-raising adventure on a large mass of floating ice. Muir’s learning in observation throughout his life led him to devote his last years to preserving the natural environment. His writing and speaking raised the awareness of the importance of conservation and helped bring about our national park system. Readers may feel they know John Muir after reading his story and may catch his passion for preserving the riches of our land. The others’ portrait of Muir’s life is a testmony to what it means to be lifelong learners and to use that learning to inform and bring about change.
19. What kind of book is the speaker introducing?
20. What do we learn about John Muir when he was young?
21. What did John Muir intend to do through writing and speaking?