Not many decisions could have been more difficult for a family to make them to say farewell to a community where it had lived for centuries, to abandon old ties and familiar landmarks, and to sail across dark seas to a strange land. Today, when mass communications tell one part of the world all about another, it is quite easy to understand how poverty or tyranny might force people to exchange an old nation for a new one. But centuries ago migration was a leap into the unknown. It was an enormous intellectual and emotional commitment. The forces that moved early immigrants to their great decision ― the decision to leave their homes and begin an adventure filled with uncertainty, risk and hardship ― must have been of overpowering proportions. As Oscar Handlin states, the early immigrants of America "would collide with unaccustomed problems, learn to understand alien ways and alien languages, manage to survive in a very foreign environment". Despite the obstacles and uncertainties that lay ahead of them, millions did migrate to "the promised land" ― America. But what was it that moved so many to migrate against such overwhelming odds There were probably as many reasons for coming to America as there were people who came. It was a highly individual decision. Yet it can be said that three large forces―religious persecution, political oppression and economic hardship-provided the chief motives for the mass migrations to America. They were responding in their own way to the pledge of the Declaration of Independence: the promise of "life, liberty and the pursuit of happiness". The search for freedom of worship has brought people to America from the days of the pilgrims to modern times. In 1620, for example, the Mayflower carried a cargo of 102 passengers who "welcomed the opportunity to advance the gospel of Christ in these remote parts". A number of other groups such as the Jews and Quakers came to America after the Pilgrims, all seeking religious freedom. In more recent times, anti-Semitic persecution in Hitler’s Germany has driven people from their homes to seek refuge in America. However, not all religious sects have received the tolerance and understanding for which they came. The Puritans of the Massachusetts Bay Colony showed as little tolerance for dissention beliefs as the Anglicans of England had shown them. They quickly expelled other religious groups from their society. Minority religious sects, from the Quakers and Shakers through the Catholics and Jews to the Mormons, have at various times suffered both discrimination and hostility in the United States. But the diversity of religious belief has made for religious toleration. In demanding freedom for itself, each sect had to permit freedom for others. The insistence of each successive wave of immigrants upon its right to practice its religion helped make freedom of worship a central part of the American Creed. People who gambled their lives on the right to believe in their own God would not easily surrender that right in a new society. The second great force behind immigration has been political oppression. America has always been a refuge from tyranny. As a nation conceived in liberty, it has help out to the world the promise of respect for the rights of man. Every time a revolution has failed in Europe, every time a nation has succumbed to tyranny, men and women who love freedom have assembled their families and their belongings and set sail across the seas. This process has not come to an end in our own day. The terrors of Hitler’s Germany and Mussolini’s Italy, the terrible wars of Southeast Asia ― all have brought new thousands seeking safety in the United States. The economic factor has been more complex than the religious and political factors. From the very beginning, some have come to America in search of riches, some in flight from poverty, and some because they were bought and sold and had no choice. And the various reasons are intertwined. Thus some early arrivals were lured to these shores by dreams of amassing great wealth, like the Spanish in Mexico and Peru. These adventurers, expecting quick profits in gold, soon found that real wealth lay in such crops as tobacco and cotton. AS they built up the plantation, economy in states like Virginia and the Carolinas, they needed cheap labor, So they began to import indentured servants from England (men and Women who agreed to labor a term of years in exchange for eventual freedom), and slaves from Africa. The process of industrialization in America increased the demand for cheap labor, and chaotic economic conditions in Europe increased the supply. If some immigrants continued to believe that the streets of New York were paved with gold, more were driven by the hunger and hardship of their native lands. The Irish potato famine of 1845 brought almost a million people to America in five years. American manufacturers advertised in European newspapers, offering to pay the passage of any man willing to come to America to work for them. The immigrants who came for economic reasons contributed to the strength of the new society in several ways. Those who came from countries with advanced political and economic institutions brought with them faith in those institutions and experience in making them work. They also brought technical and managerial skills which contributed greatly to economic growth in the new land. Above all, they helped give America the extraordinary social mobility which is the essence of an open society. In the community he had left, the immigrant usually had a fixed place. He would carry on his father’s craft of trade; he would farm his father’s land or that small portion of it that was left him after it was divided with his brothers. Only with the most exceptional talent and enterprise could break out of the circumstances in life into which he had been born. There were no such circumstances for him in the New World. Once having broken with the past, except for sentimental ties and cultural inheritance, he had to rely on his own abilities. It was the future and not the past which he had to face. Except for the Negro slave, the immigrant could go anywhere and do anything his talents permitted. A large, virgin continent lay before him, and he had only to join it together by canals, railroads and roads. If he failed to achieve the dream of a better life for himself, he could still retain it for his children. These were the major forces that started this massive migration to America. Every immigrant served to reinforce and strengthen those elements in American society that had attracted him in the first place. The motives of some immigrants were commonplace. The motives of others were noble. Taken together they add up to the strengths and weaknesses of America.In what way did immigrants seeking economic freedom contribute to the strength of the U. S. economy A．They introduced advanced political and economic institutions.B．They brought with them technical and managerial skills.C．They helped give America social mobility.D．All of these.