Starting in 1972, the National Park Service established a policy for forest fires called Natural Bum. It was true {#blank#}1{#/blank#} some forest fires, such as those which were caused by lightning were necessary for forests{#blank#}2{#/blank#} (keep) balanced ecosystems, so the fire should be allowed to burn{#blank#}3{#/blank#} , a big fire in Yellowstone National Park in 1988 caused this policy to be abandoned (放弃) since the fire was initially allowed to burn yet soon out of control. As a result, the fire of 1988 destroyed much of Yellowstone, which is America's {#blank#}4{#/blank#}(old) and most beloved national park. Massive areas of plants were destroyed, and large empty spaces and acres of burned and blackened trees greeted {#blank#}5{#/blank#} (visit). The rivers and streams were choked with ash, and the ecosystem of the park was changed {#blank#}6{#/blank#} repair.

    In addition, great numbers of animals{#blank#}7{#/blank#} (kill) by the fires that burned out of control. The fires were driven by high winds{#blank#}8{#/blank#} (move) as many as ten miles a day. Many small animals died in the flames. The fires' rapid advances {#blank#}9{#/blank#} (give) the wildlife little chance to escape. Even today, few of these small forest animals have returned to live in the park. In the years immediately following the fires, the numbers of visitors declined{#blank#}10{#/blank#} (rapid).

    The history of Chinese currency covers more than 3,000 years. Currency of some type has been used in China since the Neolithic age (新石器时代), {#blank#}1{#/blank#} can be traced back to between 3,000 and 4,500 years ago. Cowry shells (贝壳) are believed to have been the {#blank#}2{#/blank#} (early) form of currency used in Central China, and were used during the Neolithic period. The use of shell money is confirmed in the Chinese writing system. The traditional {#blank#}3{#/blank#} (character) for “goods”, “buy” and “sell”, in addition to other {#blank#}4{#/blank#} (vary) words relating to exchange, all contain the “shell”.

    Around 210 BC, the first emperor of China Qin Shi Huang (260 — 210 BC) abolished all other forms of local currency and introduced{#blank#}5{#/blank#} uniform copper coin. Although paper money {#blank#}6{#/blank#} (invent) in China in the 9th century, the base unit of currency remained the copper coin. Copper coins were used{#blank#}7{#/blank#} the chief currency in China until the {#blank#}8{#/blank#} (introduce) of yuan in the late 19th century.

    Currently, the RMB is the official currency of China. With over 1.3 billion people {#blank#}9{#/blank#} (use) RMB every day, it is one of the most commonly used currencies in the world. Nowadays, online payment is taking a large share in the market. Will paper money disappear one day like shells or copper coins {#blank#}10{#/blank#} (replace) by a new way of payment? Only time can tell.

    All {#blank#}1{#/blank#}. Soon after the quakes, the army sent 150,000 soldiers to Tangshan to help the rescue workers. Hundreds of thousands of people were helped. The army organized teams to {#blank#}2{#/blank#}and to bury the dead. {#blank#}3{#/blank#}the city, most of the 10,000 miners were rescued from the coal mines there. Workers built shelters for survivors whose homes had been destroyed. Fresh water was taken to the city by train, truck and plane. Slowly, the city began to breathe again.

    My name is Elias. I am a poor black worker in South Africa. {#blank#}4{#/blank#} I first met Nelson Mandela was a very difficult period of my life. I was twelve years old. It was in 1952 and Mandela was the black lawyer to whom I went for advice. He offered guidance to poor black people on their legal problems. He {#blank#}5{#/blank#} his time, for which I was grateful.

    I've always been attracted by the {#blank#}1{#/blank#} (beautiful) of Chinese culture and its vast history. When we first arrived in China, my friend Tony and I expected a huge city {#blank#}2{#/blank#} (fill) with modern buildings, busy streets and a crowded transport system. But we were pleasantly surprised.

    The first thing {#blank#}3{#/blank#} struck us was the space. Yes, Beijing is indeed huge, but its wide streets and green spaces made every area feel less crowded. Tian'anmen Square was the perfect example of this. The Forbidden City was {#blank#}4{#/blank#} (surprise) clean and well preserved. Everywhere we looked, there were people {#blank#}5{#/blank#} (tidy) and cleaning, which really left an {#blank#}6{#/blank#} (impress) of national pride. We {#blank#}7{#/blank#} (concern) that few people would speak English, even in Beijing. But we found it common for Chinese people to know a few words of English. The most exciting part of our visit was riding around in the sunshine and exploring the city {#blank#}8{#/blank#} Ofo bikes.

    It was great {#blank#}9{#/blank#} (experience) Beijing's landmarks in person after admiring {#blank#}10{#/blank#} for so many years. This was our first visit to China, but certainly not our last.

When talking about our bodies, we often forget our skin. Actually, our skin is very important, too. It keeps us{#blank#}1{#/blank#}(inform) of the outside world--{#blank#}2{#/blank#}it is hot or cold, wet or dry.

Try this: pull up the skin from the back of your hand and then let {#blank#}3{#/blank#}go. What happens?

The skin goes back to its first position, which means that skin is elastic (有弹性的).

Our skin seems to be very thin, but it {#blank#}4{#/blank#} (make) up of two layers. The top layer is the one we wash every day. Do you know that this part of skin is dead? However, it is still very important because it serves as{#blank#}5{#/blank#} (protect) against dirt and disease.

Skin has millions of tiny holes called pores(毛孔). Pores allow liquid, especially sweat,{#blank#}6{#/blank#}(pass) through. By{#blank#}7{#/blank#} (sweat), our bodies keep up a normal temperature. When it is very hot, we sweat a lot, but{#blank#}8{#/blank#}(strange) enough, when it is quite cool, we also sweat. On a cool day, our bodies produce {#blank#}9{#/blank#}average of 700 ml of sweat. That is{#blank#}10{#/blank#}(much) than 0.5 kilos.