Read the following passage and mark the letter A, B, C, or D on your answer

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 44 to 50.
Humans first lived on Earth 40,000 years ago in Africa. How they arrived in the Americas is a subject of debate among anthropologists. The most accepted explanation today is the Bering Strait land bridge theory. Recent evidence, however, supports the view that migration occurred by other routes as well.
The Bering Strait is a narrow passage between Siberia in Russia and Alaska to the west of Canada. In 1856, Samuel Haven proposed that about 20,000 years ago during the Ice Age, the sea level dropped when the water became locked up in glaciers. The level was about sixty meters lower than it is today. This exposed the land beneath the strait, allowing humans and animals to walk from Siberia to Alaska. Evidence for this land bridge is confirmed by soil cores taken from the waters of the strait, showing that the land during that era was dry plains. Remains of large mammals have also been found, suggesting that Asian tribes were hunters who followed the animals into North America about 12,000 years ago. Mammals native to Africa and Asia, such as lions and cheetahs, later evolved in North America into extinct species. And the North  American camelid, which became extinct in North America, evolved into camels in Asia.
The archaeological record shows that the migration went from west to east. The land bridge was about 2,000 kilometers wide. From Alaska, these nomadic hunters moved down into North America by following ice-free routes along the Pacific coastline. Some groups then made their way eastward past the Rocky Mountains and all the way to the Atlantic coast. Other tribes continued south into Central and South America.
The people who crossed the Bering Strait are called the Clovis people after the town of Clovis, New Mexico, where their spear points were found in 1932. Clovis points have a distinctive shape. Similar points  have been found as far east as the east coast of the United States and as far south as Chile. Some scientists  theorize that the Clovis people who crossed the Bering Strait continued to all parts of North and South  America.
But evidence has also been found that some humans arrived at least 1,000 years before the Clovis people. These findings have caused some to believe that the Americas also may have been populated by a route other than the Bering Strait, perhaps by boats crossing the South Pacific. Archaeologists have found indications that boats were used in Australia and Japan as far back as 25,000 to 40,000 years ago. They speculate that some could have sailed to the coast of the Americas and then down the Pacific coast. Unfortunately, many potential coastal sites are now under water, making it difficult to search for signs left by ancient sailors.
Measurements of human skeletons also point to multiple sources of migration. Native Americans have broad faces and prominent cheekbones that match those of Asian people. But other skulls have been found  with narrow skulls and flattened faces, consistent with Polynesians and Europeans.
Recent studies in molecular genetics confirm that American Indians share an Asian origin. But a newly discovered DNA line has shown a non-Asian influence as well. DNA research has also revealed that Americans may have diverged genetically from Siberians 20,000 years ago, much earlier than the archaeological evidence indicates.