题目内容：
阅读材料，回答题。The National Trust The National Trust in Britain plays an increasingly important part in the preservation for public enjoyment of the best that is left unspoiled of the British countryside. Although the Trust has received practical and moral support from the Government, it is not a rich government department. It is a voluntary association of people who care for the unspoiled countryside and historic buildings of Britain. It is a charity which depends for its existence on voluntary support from members of the public. Its primary duty is to protect places of great natural beauty and places of historical interest.
The attention of the public was the first drawn to the dangers threatening the great old houses and the castles of Britain by the death of the Lord Lothian, who left his great seventeenth-century house to the Trust together with the 4500-acre park and estate surrounding it. This gift attracted wide publicity and started the Trust's "Country House Scheme" Under this scheme, with the help of the Government and the general public,the Trust has been able to save and make accessible to the public about 150 of these oil houses. Last year, about1.75 million people paid to visit these historic houses, usually at a very small charge.
In addition to country houses and open spaces, the Trust now owns some examples of ancient wind and water mills, nature reserves, 540 farms and nearly 2,500 cottages or small village houses, as well as some complete villages. In these villages no one is allowed to build, develop or disturb the old village environment in any way and all the houses are maintained in their original 16th century style. Over 4,000 acres of coastline,woodland, and hill country are protected by the Trust and no development or disturbances of any kind are permitted. The public has free access to these areas and is only asked to respect the peace, beauty and wildlife.
Over the past 80 years the Trust has become a big and important organization and an essential and respected part of national life. It helps to preserve all that and of historical significance not only for future generations of Britons but also for the millions of tourists who each year invade Britain in search of a great historic and cultural heritage.
The National Trust is a__________. A．Government agency depending on voluntary services
B．Non-profit organization depending on voluntary services
C．Government department but is not rich
D．Private organization supported by the government
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