The geography of the Arctic Circle makes it a tough place to call home. In the winter, the nights【小题1】（length）until the sun barely shines. In the extreme north, the ground is permanently frozen. The hardy Inuit（因纽特人）【小题2】（be）the native people of northern Alaska, Canada and Greenland.【小题3】（traditional）, they hunted Arctic animals for food, especially caribou（驯鹿）, seals and whales. The Inuit used animal skins for clothing and for shelter.

Most traditional Inuit【小题4】（family）had both a summer and a winter home. During the summer, many Inuit lived in tents【小题5】（cover）with caribou or seal skins. In the winter, some Inuit built snowhouses,【小题6】provided shelters from freezing temperatures. They could construct【小题7】snowhouse in about two hours. To begin, they cut hard-packed snow into blocks. The blocks were from 2 to 3 feet long and 1 to 2 feet wide. Next, the blocks【小题8】（pile）together perfectly into a spiral（螺旋形）. The spiral was wound upward in smaller and smaller circles to form the dome-shaped（圆顶形的）home. On top of the dome, a hole was cut out to provide fresh air. Finally, the Inuit dug an entrance【小题9】the snowhouse.

Today, most Inuit live in modern housing. But the tradition of【小题10】（build）snowhouses is still passed down from one generation to another.

Over the centuries, farmers 【小题1】 (discover) thousands of different species of food crops. Each species has special qualities. To feed the seven billion people on Earth, most farmers today are growing only species of plants that are easy 【小题2】(produce) in large numbers. Meanwhile thousands of other species are becoming extinct. For example, in China, 90 percent of the wheat 【小题3】 (vary) grown just a century ago have disappeared.

One solution 【小题4】 this problem is to collect and preserve the seeds of as many different species as we can 【小题5】 they disappear. This idea 【小题6】 (suggest) for the first time by Russian scientist Nikolay Vavilov. In 【小题7】 1920s and 1930s, he collected around 400,000 seeds from five continents. There are now around 1,700 seed banks in countries around the world. The Svalbard Global Seed Vault, which preserves almost one million seed samples, has one of the 【小题8】 (large) collections.

In the US, Diane Ott Whealy and her husband founded Heritage Farm, a place 【小题9】 people can store and trade seeds. By doing this, they are reintroducing foods into the marketplace 【小题10】 haven’t been grown for years.