A、Because he was locked up in a mental hospital. B、Because he had difficulties in walking. C、Because he lived far away from Oxfo

In 1879, Oxford University in England asked Prof. James Murray to serve as an editor for what was to be the most ambitious dictionary in the history of the English language. It would include every English word possible and would give not only the definition but also the history of the word and quotations showing how it was used.
    This was a huge task, so Murray had to find volunteers from Britain, the United States, and the British colonies to search every newspaper, magazine and book ever written in English. Hundreds of volunteers responded, including William Chester Minor. Dr. Minor was an American surgeon who had served in the Civil War and was now living in England. He gave his address as "Broadmoor, Crowthorne, Berkshire", 50 miles from Oxford.
     (16)Minor joined the army of volunteers sending words and quotations to Murray. Over the next years, he became one of the staffs most valued contributors. But he was also a mystery. In spite of many invitations, he would always decline to visit Oxford. So in 1897, Murray finally decided to travel to Crowthorne himself.(17)When he arrived, he found Minor locked in a book-lined cell at the Broadmoor mental hospital for the criminally insane.
    Murray and Minor became friends, sharing their love of words. Minor continued contributing to the dictionary, sending in more than 10,000 entries in 20 years. Murray continued to visit Minor regularly, sometimes taking walks with him around.(18)Minor died in 1920, seven years before the first edition of the Oxford English Dictionary was completed.
16. How did Minor contribute to the dictionary?
17. Why did Minor refuse Murray’s invitations?
18. What do we learn about Minor?