Speculation as to how man found his way to America was lively at the outset, and the proposed routes boxed the compass. With one or two notable exceptions, however, students of American anthropology soon settled for the plausible idea that the first immigrants came b way of a land bridge that had connected the northeast comer of Asia to the northwest corner of North America across the Bering Strait. Mariners were able to supply the reassuring information that the strait is not only narrow – it is 56 miles wide – but also shallow, a lowering of the sea level there by 100 feet or so would transform the strait into an isthmus (地峡). With little eels in the way of evidence to sustain the Bering Strait land bridge, anthropologists (人类学家) embraced the idea that man walked dryshod (不湿鞋的) from Asia to America.
Toward the end of the last century, however, it became apparent that the Western Hemisphere was the New World not only for man but also for a host of animals and plants. Zoologists and botanists showed that numerous subjects of their respective kingdoms must have originated in Asia and spread to America. These findings were neither astonishing nor wholly unexpected. Such spread of populations is not to be envisioned as an exodus or mass migration, even in the case of animals. It is, rather, a spilling into new territory that accompanies increase in numbers, with movement in the direction of least population pressure and most favorable ecological conditions. But the immense traffic in plant and animal’s forms placed a heavy burden on the Bering Strait land bridge as the anthropologists ahead envisioned it. Whereas purposeful men could make their way across a narrow bridge, the slow diffusion of plant and animals would require an avenue as a continent and available for ages at a stretch.
1.The movement of plants and animals form Asia to America indicates ______.
A.that they could not have traveled across the Bering Strait
B.that Asia and the Western hemisphere were connected by a large land mass
C.that the Bering Sea was an isthmus at one time
D.that migration was in the one direction only
2.The author is refuting the notion that _____.
A.life arose in America independently of life in Europe
B.the first settlers in America came during the sixteenth century
C.a large continent once existed which has disappeared
D.man was a host to animals and plants
3.By using the words “boxed the compass “(in Line 7) the author implies that _____.
A.the migration of mankind was from West to East
B.the migration of mankind was from East to West
C.mankind traveled in all directions
D.mankind walked from Asia to America
4.One reason for the migration not mentioned by the author is _____.
B.favorable environmental conditions
D.the existence of a land bridge
5.We may assume that in the paragraph that follows this passage the author argues about______.
A.the contributions of anthropologist
B.the contributions of zoologists and botanists
C.the contributions made by the American Indians
D.the existence of a large land mass between Asia and North America