题目内容：

Dogs were living as companions to the early settlers of North America over 10,000 years ago.

The oldest domestic dogs in the Americas were thought to be around 9500 years old. Angela Perri of Durham University, UK, and her colleagues have carried out fresh radiocarbon dating on the two dog skeletons that gave this date, discovered in the prehistoric Koster site in Illinois, and found they were even older: around 10,100 years old.

A third dog from another Illinois site called Stilwell II was older still，at 10,190 years old. That makes it the oldest known domesticated dog in the Americas.

The team concluded that all three dogs were domesticated as their skeletons were complete and unskinned, and so hadn’t been butchered for food. They had also been carefolly buried, evidence they were valued by their owners. The Stilwell II dog, which probably resembled a small English settler, was under what seemed to be the floor of a living area.

It is unclear why it took so long for tame dogs to arrive in the Americas, given that they were domesticated at least 14,000 years ago in Eurasia. By this time, people were already moving into North America from Siberia; there is evidence some reached Chile 18,500 years ago. Geneticists have found signs of at least three waves of migration over the following millennia. There is no evidence that domestic dogs accompanied them.

“We don’t know if dogs were part of the first waves of immigration to the Americas” says Luc Janssens of Ghent University in Belgium. “It could be so, but no archaeological bones have yet been found.”

It is “overwhelmingly probable” that some of the early settlers did bring dogs to the Americas, but they may not have had “the time or the spiritual compulsion to bury them’％ says Pat Shipman of Pennsylvania State University.

1.How old is the oldest known domestic dog in the Americas?

A. About 9500 years.    B. About 10,100 years.

C. 10,190 years.    D. 18,500 years.

2.The underlined word “butchered” in the fourth paragraph could be replaced by .

A. killed    B. bought

C. trained    D. raised

3.What is the attitude towards when tame dogs arrived in the Americas in the last three paragraphs?

A. Undoubted.    B. Unsure.

C. Indifferent.    D. Unconfident.

4.What is the main topic of this passage?

A. The earliest domestic dog in the Americas.

B. The first dog arriving in the Americas.

C. How dogs were domesticated in the Americas.

D. When the oldest dog was found in the Americas.