Directions: Complete the following passages by using the words in the box. Each word can only be used once. Note that there is one word more than you need.

A. selected        B. distinctive     C. signature       D. odds     AB. domestication       AC. decided AD. individuals   BC. tamest     BD. conflicted     CD. mixed     ABC. develop

If you see a house cat, the【小题1】are high that it will have white paws, a look that many owners affectionately call“socks.” But socks are rarely seen in wildcats, the elusive and undomesticated cousin of the house cat, so why do so many pet cats sport furry white feet?

As it turns out, this story started about 10,000 years ago, when humans and cats 【小题2】   life was better together.

This【小题3】eventually led to uber-prevalent socks on cats, as well as other well-known coat patterns, said Leslie Lyons, professor emerita and head of the Feline Genetics Laboratory at the University of Missouri College of Veterinary Medicine.

“As humans became farmers and started staying in one place, they had grain stores and waste piles” that attracted rodents, Lyons said. It was a mutually beneficial arrangement: the humans had fewer rodents to deal with and the cats got an easy meal.

The wild, undomesticated ancestor species of house cats, Felis silvestris, lives in Africa and Eurasia. These felines are tasty snacks as kittens and stealthy predators as adults, so 【小题4】 born with a coat that offers camouflage (保护色) have tended to survive and reproduce.

But not every F. silvestiis is born with a coat that blends into its habitat.

“Genetic mutations are occurring all the time.” Lyons said.

There isn’t much evidence to indicate why early cat people chose the individuals they did, but Lyons said the range of coats seen on modern domestic cats shows that our agrarian ancestors favored cats with markings that would have 【小题5】with their camouflage.

In its native mixed forest or scrub desert environment, a cat with stark white paws would have stood out to predators and prey.

When humans started taking an interest in cats, these white paws would have stood out to them, too. “There were probably people saying, ‘I particularly like that kitten because it has white feet . Let’s make sure it survives’”, Lyons said.

Humans probably also【小题6】cats who were calm and comfortable around humans, Lyons said. Behavioral traits seem unrelated to coat color, but for reasons that scientists don’t fully understand, white spots tend to appear when the 【小题7】individuals are selected and bred.

These【小题8】fur colors and markings emerge while a cat embryo is developing. The cells that give cat fur its color first appear as neural crest cells, which are located along what will become the back, Lyons said.

Then, those cells slowly migrate down and around the body. If those waves of cells move far enough to meet each other on the cat’s front side, the embryo will be born a solid-colored kitten, such as an all-black or all-orange cat. Felines 【小题9】white feet, faces, chests and bellies when these cells don’t quite make it all the way.

So, the next time you see a kitty wearing white socks, you’ll know that this 【小题10】 feature is a result of genetic mutations, domestication and developmental biology. Although if you try telling the cat that, it will probably just look at you quizzically before sauntering away.