4．Why are visitors required to turn off their mobile phones?

　　A．To ensure the safety of others.

　　B．To ensure the security of the Castle.

　　C．To prevent them from disturbing others.

　　D．To prevent the use of the built­in cameras.

　　C　[细节理解题。从倒数第二个小标题下面的最后一句"Mobile phone must be switched off inside the State Apartments and St George's Chapel in consideration of other visitors."可知答案。]

　　B

　　There are around 6，000 living languages in the world-and at least half of these are in danger.In every part of the world, languages are disappearing.In fact, one scientist has said that languages are in more danger of extinction than birds or mammals.Professor Steve Sutherland of the University of East Anglia says that in the past 500 years 4.5 percent of languages have died out-compared with 1.3 percent of birds，and 1.9 percent of mammals.

　　Languages come and go，and thousands have done exactly that without leaving any trace (痕迹). Only a very few-Basque，Greek and Latin among them-have lasted more than 2，000 years.But it seems that the pace of their disappearance is becoming quicker.

　　The Ethnologue，a database of all the languages spoken in the world，states that 417 languages are spoken by so few people that they are in the final stages of becoming extinct.If very few people speak a language，it will probably die out.

　　Languages may be lost through migration (迁移)，as people move from small towns to city centers，or when environments are destroyed by the search for oil or wood. Natural disasters can also devastate populations，and along with them，their language.Governments also play a role in the extinction of languages. The need to establish "official languages"，for a country to educate its children and carry out its business, had a disastrous effect on many small languages.

What is lost if a language is lost? Some people argue that languages die as the human race develops.Obviously there could be great benefits if everyone in the world