Yellow River Valley is the birthplace of ancient Chinese     1    （civilize）, and for that reason the Yellow River is often called "Mother River." The valley     2    （surround）the principal river of northern China and is at the center of thousands of years of Chinese history. It is called the Yellow River     3     its waters carry soil, which gives the river     4    （it）yellow-brown color, and when the river overflows, it leaves a yellow residue（残留）behind. While the river helps create fertile land that is suitable     5     farming, during certain times of the year the Yellow River frequently overflows. The water damages     6    （house）and crops across the North China Plain, an important     7    （agriculture）region. For thousands of years, the Chinese have carried out major public work projects     8    （control）the water from the Yellow River. Despite the possibility of flooding, many of China's cities,     9    （situate）along the river, are growing increasingly in the valley,     10     have become the center of Chinese culture, society, and learning.

2 . When you think of the Arctic, you imagine an icy land of pure white snow, which is considered to be the last really clean place     1    (leave) on Earth. Yet plastic trash has now reached the remote regions of the Arctic and the Alps. A team of     2    (scientist) has discovered large quantities of microplastics(微塑料) — very small pieces of plastic waste — in the Arctic snow. While microplastics have been found in sea-water, drinking water, and even in animals over     3     past several years, this is the first study to show microplastics in snow,     4     indicates it is an airborne pollutant that must be paid attention to.

The researchers state that microplastics in snow suggest that microplastics may be in the air that we     5    (breath). Therefore, it is really important     6    (assess) if microplastics also reach lung tissues.

Previous research has found that they flow over long distances and into our oceans,     7    (damage) ecosystems along the way. They start in our wastewater, when we wash clothes     8     plastic fibers. The wastewater then flows into rivers and out to sea, where they     9    (eat) by sea animals. If people then eat these animals, it means that we’re     10    (probable) eating the plastic as well.

I wake up to the sound of the wind buffeting the cloth of my tent. Even though the sun is    1    (bright) shining, telling whether it is morning or night is impossible. I’m above the Arctic Circle,    2    in summer the sun never sets. I’m in the remote far north of Sweden in Sarek National Park,    3    place with no roads or towns.

Around 9,000 years ago, reindeer began to arrive at Sarek’s mountains. Following the reindeer    4    (be) the Sami people, who made this territory their home. In 1909, Sarek was made a national park    5    (keep) the land in its natural state.

For hundreds of years,    6    (look) after reindeer was a way of life for the Sami. Today, most Sami have houses in villages near Sarek and live a modern life just    7    their neighbours and enjoy their    8    (tradition) as before.

After breakfast, I pack my bag and set out again. Being in such a    9    (beauty) and wild place makes me feel    10    (bless) to be alive.

It's long been known for its beautiful architecture, large quantities of green spaces and     1    （tradition） coffee shops — and now Vienna is building itself a reputation for something even more pleasing.

The Austrian capital has been ranked the world's most livable city for the second year running,     2     （reach） the top with almost perfect scores for stability, culture and environment, education and construction, and health care.

The index considers more than 30 qualitative （定量的）factors ranging five broad     3    （category） , the data as follows: stability （25%）, healthcare （20%）, culture and environment （25%）, education （10%） , and infrastructure （20%）.

Lucie Lamster Thury,     4       New Yorker who moved to Vienna in 2004 and runs shopping tours of the city, said Vienna "taught me how to live".

“Coining from Manhattan it was hard to slow down but I love the pace of Vienna. It's     5     （relative） quiet, clean and culturally abundant, and I've never felt     6     （safe） in Europe or in the States. ”

“I thought I'd never get used to shops being closed on Sundays, but it     7     （change） my life — people actually get to rest here, and private life is as important as work. ”

It was followed by Melbourne,     8    Vienna bettered last year after Melbourne was at the top seven years.

Sydney, Osaka and Calgary make     9    the top five on the annual Global Liveability Index of 140 cities around the world,     10    （collect） by The Economist Intelligence Unit.

Antarctica is the coldest continent on Earth. It's also among the driest.     1    (cover) about 14 million square kilometers around the South Pole, it is the fifth     2     (large) continent in the world. A high mountain range, the Transantarctic Mountains,     3     (run) from east to west, cutting the continent into two. There are    4    (volcano) too, but they are not very active. Antarctica holds about 90% of the world's ice, and most of its fresh water is in a frozen state, of course. Approximately 98% of the surface is covered     5     (permanent) by the ice cap. On average it is around two kilometers thick, but in some places it reaches a     6     (deep) of about five kilometers. Strong winds driven by gravity blow from the pole to the coastline, while other winds blow round the coast. It is difficult     7     (imagine) a more inhospitable place.

Yet Antarctica is full of wildlife, which has adapted     8     its extreme conditions. But the Antarctic winter,     9     involves a period of over three months of complete darkness, as well as the extreme cold and lack of rainfall, means that few types of plants can survive there. Only two types of flowering plants are found,     10     there are no trees on the large continent.