There are two main     1    (reason) why the temperature of the air is always     2    (change). One reason is that the air around you     3    (move) in from somewhere else. Air usually moves in large bodies     4    (call) air masses. Some air masses move in from the north. These air masses usually have cold air that causes the temperature     5    (drop). Air masses also move in from the south. They usually have warmer air that causes the temperature to rise.

Temperature changes during the day or night can be great     6    small. This depends    7    (part) on how many clouds are in the sky.     8    there are many clouds during the night, they act like covers on your bed. They blanket the earth and keep the air from     9    (lose) much of its heat. The temperature usually does not drop much during such a night. When there are many clouds during     10    day, some of the sun’s energy will not reach the earth. The temperature usually does not rise much on such a day.

After eating a diet of bread, hamburgers and spaghetti for three     1    (month), I began to miss Chinese food. Luckily, in     2     international city like New York, I have little difficulty     3    (find) a Chinese restaurant. However, the Chinese food, which the locals consider as their favorite, is not exactly the Chinese food I enjoy in Beijing. I can always find such so-called “Chinese food” as honey chicken on the menu,     4     I actually have never even heard of it before.

One day, I went to a Chinese restaurant     5     my local friends. After the meal, each of us     6     (give) a dumpling-shaped cookie. Once I bit into it, I realized something not quite right. I found a piece of paper with a message that read, “This fortune’s no good, try another. ” At first I     7     (think) it must be a trick of the restaurant. When I told this to my friends, they burst out     8    (laugh) and asked, “Are you really from China? ” 

But it doesn’t mean there is no place in New York where I can satisfy my stomach. I always head to China Town when I     9    (extreme) miss the food of my homeland.     10    (follow) the hot and spicy smell, I can always find the most Chinese food that excites me in the city.

It took years     1    (complete) the Qinghai-Tibet Railway. The construction workers     2    (overcome) the most difficult engineering challenges，one of which was how to protect the delicate ecosystem.To allow the wild animals to move safely and freely in their     3    (nature) habitat，they built thirty-three passages under the railway. To prevent damage to wetlands and grasslands，675 bridges with a total length of about 160 kilometres     4    (build) between Golmud and Lhasa. They even moved 140，000 square metres of wetland to     5     new area in order to protect its distinct ecosystem.     6    (locate) at over 5，000 metres above sea level，Tanggula Station is the highest railway station in the world. In locations such as this，the thin air，changeable weather and high levels of UV radiation presented perhaps the     7     (great) challenge for railway workers. To make sure they stayed healthy，several oxygen-making stations were constructed. To protect Cuona Lake     8     construction waste，the railway workers used thousands     9     thousands of sandbags to build a twenty-kilometre wall along the lake. In a word，the railway workers built our “impossible” railway with the care that the environment deserves. It     10    (true) is an extraordinary “Sky Railway”.

Beijing and large areas of northern China woke to     1     (choke) sand and dust, as a winter sandstorm sent many of the air pollution     2     (level) off the charts.

The sandstorm originated in Mongolia and     3     (gradual) moved south, covering much of northern China, from the eastern city of Tianjin to Xinjiang region in the far west. The sandstorm is expected     4     (last) for two days.

In the spring of 2021, Beijing was hit by the biggest sandstorm in nearly a decade,     5     turned the skies a shade of orange. In previous decades, each May     6     (see) at least two rounds of sandstorms. The     7     (frequent) and severity of sandstorms was partly due to drought, growing population pressure and poor progress in revegetation (再种植), which caused rapid desertification of land in the north and northwest. But sandstorms     8     (decrease) sharply ever since. The annual number of sandstorm-affected days in Beijing fell     9     a peak of 26 days in the 1950s to just three days after 2010.

Since 2000, the Chinese government has spent billions of dollars on sandstorm prevention, started     10     (vary) reforestation and ecological projects and sent up satellites to monitor sandstorms and alert weather agencies ahead of time.