The Huang He Valley, also 【小题1】 (refer) to as the Yellow River Valley, was the birthplace of ancient Chinese civilization, because of 【小题2】 it is often called “Mother River”. The valley is at the center of thousands of years of Chinese history. 【小题3】 China’s second-longest river, the Huang He is over 5, 400 kilometers long. It is called the Yellow River because its waters carry sand and mud, 【小题4】 (give) the river its yellow-brown color.

While the river helps create fertile land that is suited for farming, during certain times of the year the Huang He 【小题5】 (frequent) overflows, which damages housing and crops across the North China Plain, 【小题6】 important agricultural region. For thousands of years, the Chinese 【小题7】 (conduct) major public projects to keep control of the water from the Huang He, including hydroelectric dams in modern times. Despite the possibility of flooding, the Huang He Valley basin is home to a huge population, and many of the country’s oldest cities 【小题8】 (locate) along the river.

Tribes and villages appeared from around 2100 BC to 1600 BC in the Huang He Valley. During that time, tribal leaders came together to solve the problem of the Huang He overflowing and wiping out their villages and crops. With the ability 【小题9】 (control) the Huang He better and save their crops from flooding, a number of 【小题10】 (dynasty) were then headquartered in the region. The valley became the center of Chinese culture, society and learning.

The city-state is usually a small, independent country 【小题1】( consist) of a single city, the government of which exercises full power within its borders. The single city of city-state functions as the center of political, economic, and 【小题2】 (culture) life.

Historically, the first recognized city-states developed 【小题3】(gradual) in the classical period of Greek civilization during the 4th and 5th centuries BC. The Greek term for city-states, “polis”, came from the Acropolis,【小题4】 served as the governmental center of ancient Athens. City-states became active again during the l1th century， when several Italian cities, such as Naples and Venice, 【小题5】(realize) considerable economic boom.

The unique characteristic of a city-state that sets it aside from other 【小题6】(type)   of governments is its independence. This means that a city-state has the full right and power to govern itself and 【小题7】 (it) citizens, without any interference (干涉) from outside governments. For example, the government of the city-state of Monaco, though【小题8】(locate) totally within France, is not subject to French laws or policies.

Unlike ancient city-states, modern city-states remain small in land areas. Lacking the space necessary for agriculture or industry, the economies of the three modern city-states depend【小题9】 trade or tourism. Singapore, for example, has 【小题10】 second-busiest seaport in the world, and Monaco and Vatican City are two of the world's most popular tourist destinations.

Those who make great discoveries must often overcome many challenges along the way—as was the case with the explorer Christopher Columbus. Columbus was born in 【小题1】 port city of Italy in 1451. As a teenager, he loved sailing and showed interest in geography, 【小题2】 inspired him to begin his career as a seaman.

Columbus insisted on 【小题3】 (search)for a direct route to the East Indies by sailing across the Atlantic ocean. After continuous attempts, he received 【小题4】 (finance)support from the King and Queen of Spain. On 3 August 1492, he 【小题5】 (depart)with three ships carrying about 90 crewmen. The journey was full of challenges: it took longer than expected, they faced a shortage of food and one of the ships was leaking badly, which put everyone on this ship 【小题6】 grave danger. The men on board were in panic. Regardless of all the challenges, Columbus managed 【小题7】 (keep)everyone out of danger with his knowledge and bravery across the ocean. Finally, on 12 October, the crew spotted land in the distance. Columbus called the natives living on the islands Indians because he 【小题8】 (convince)that he was in the East Indies. 【小题9】 , the shores they had reached were of the Caribbean, not the East Indies.

The major contribution of this great explorer is that he “discovered” the New World. His discovery inspired other 【小题10】 (explorer)around the world. His voyages opened a new chapter of the Age of exploration, a period which witnessed many important geographical findings.