题目内容：

In the late 1950s, a Russian geneticist called Dmitry K. Belyaev attempted to create a tame (驯化的) fox population. Through the work of a breeding programme at the Institute of Cytology and Genetics at Novosibirsk, in Russia, he sought to find the evolutionary pathway of tame animals. His test subjects were silver-black foxes, a melanistic (带黑色的) version of the red fox that had been bred in farms for the color of their fur.

He selected the animals based on how they responded when their cage was opened. About 10% of the foxes displayed a weak “wild-response”, meaning they were docile around humans. Those that hid in the corner or made aggressive voices were left in the farm. Of those friendly foxes, 100 females and 30 males were chosen as the first generations of parents.

When the young foxes were born, the researchers hand-fed them. They also attempted to touch or pet the foxes when they were two to two-and-a-half months old, for strictly measured periods at a time. If the young foxes continued to show aggressive response, even after significant human contact, they were thrown away from the population—meaning they were made into fur coats. In each selection, less than 10% of tame individuals were used as parents of the next generation.

By the fourth generation, the scientists started to see dramatic changes. The young foxes were beginning to behave more like dogs. They wagged their tails and “eagerly” sought contact with humans. By 2005-2006, almost all the foxes were playful, friendly and behaving like domestic dogs. The foxes could “read” human hints and respond correctly to gestures or glances.

1.What do we know about Belyaev’s breeding plan?

A. It explains how red foxes were bred.

B. It focuses on how tame animals evolved.

C. It explains why pet foxes became popular.

D. It concentrates on why tame animals disappeared.

2.How did he choose his test foxes in the experiment?

A. By appearance.

B. By color.

C. By reaction.

D. By flexibility.

3.What can be inferred from Paragraph 3?

A. Smart foxes were used for testing.

B. The purpose of selection was unclear.

C. Friendly foxes were kept on testing.

D. The selection was not exact and thorough.

4.What is the distinguishing characteristic of the fourth generation foxes?

A. Behaving in a friendlier way.

B. Eating plants.

C. Having drooping ears.

D. Having shortened legs.