水是人类的宝贵资源，但水被污染后给人类带来灾难．____ 、____

____ 是造成水体污染的主要原因．

看              是认识学校最好的方法。 （   ）

    Welcome to London! Now let me tell you something about this wonderful city. London, the capital of the United Kingdom, is the biggest city in Western Europe with over 7 million people. It sits by the River Thames. London has a history of more than 2,000 years. People all over the world are familiar with the city's red double-decker（双层的）buses and black taxis.

People

    The British Empire used to rule around the world, so many people from around the world moved to London. They have brought with them their own languages and cultures. More than 300 different languages are spoken in London.

Culture

    London is known for its museums. One important museum is British Museum. It is the oldest public museum in the world. There are two main art museums in London: the National Gallery and the Tate Gallery. Besides, London is also home to arts, such as theatre and music. The Globe Theatre, which was popular in the late 16th and early 17th centuries, was opened for performances of William Shakespeare's Central London.

Tourist attractions

    London has many wonderful places to visit. For example, the well-known Clock Tower, a 320-foot-high tower, was called the Big Ben. Another famous London building is Buckingham Palace. The members of royal（皇家的）family of England live there. Besides, Hyde Park is the largest open area in central London.

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向粮仓充加二氧化碳可以延长粮食贮藏期的原因是（  ）