根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
The First Americans
There was a time long ago when a land bridge connected Asia and North America. The first settlers in North America crossed this land bridge from what is now Siberia to Alaska. The people who made this initial crossing were probably following the animals they used for food.
Finally, the oceans rose and the land bridge between the continents disappeared. The settlers, who I shall call the “First Americans”， could not return to their homeland.____
For the next few thousand years, the First Americans moved south and east throughout North and South America. They made the journey all the way from Alaska to the southern tip of South America, a distance of more than 10,000 miles.____
In the far north, above the Arctic Circle, the First Americans became hunters of the ocean.____In the summer, they gathered berries and other plants. In the winter, they stayed in lodges much of the time preparing for the next summer. It was a hard life, but they learned to survive in these terrible conditions.
Farther south, in what is now Arizona, Utah, Colorado, and New Mexico, the First Americans became cliff dwellers. They began by living in caves that already existed in the cliffs.____The dwellings they built in many ways resembled today's apartment buildings.
____ They built a system of dams and canals so they could store and use water almost any time of the year. They were so successful that they could raise fruits and vegetables that were not found naturally in the desert.
A．They also discovered foods like corn and potatoes.
B．Along the way, they established many different civilizations.
C．They discovered how to add to the caves by building structures of wood and stone.
D．People living near each other tended to share similar environments and customs.
E．They built boats of animal skins and hunted or fished for their food.
F．They would have to survive in the New World they had discovered.
G．The First Americans of the Southwest learned to water the desert.
