题目内容：

There is an English saying that says, “Let Sleeping Dogs Lie.” It means not bringing up an old problem. Researchers in Hungary have found another reason to let dogs keep on sleeping. It seems the animals are learning while they sleep.

The Hungarian researchers placed tools on the dogs’ heads to know about electrical activity in the brain. The brain activity, called sleep spindles(梭状波), takes place in human begins, and has been connected with learning. The researchers hope to understand how the dogs’ ability to learn and remember changes as they get older. The study may help them understand how human brains change as we age.

The researchers found differences between male and female dogs. Iotchey, a researcher, says the females appeared much better at learning new things. Female dogs have about twice as many spindles per minute as male dogs, they also happen to be the better learners, and they memorize the task much better. But it was harder for all the older dogs to remember things, especially when several things were happening at the same time.

DoraSzabo also studies sleep spindles. Szabo is a neuroscientist in a university in Budapest. She says the older dogs have fewer spindles and are easily cheated. “If you first hide the reward into one bowl, then in another and in another, they get lost after a while. So their performance is going down, and they are getting poor in solving new problems.”

Researchers hope the study will not only help understanding of learning ability and memory changes in dogs, but also the aging of humans. Senior Researcher EnikoKubinyi adds that the aging dogs suffer from the same problems as humans who are aging. “Among very old dogs, up to two thirds of them show signs of dementia(痴呆), and this dementia is really very similar to that of humans, so we could use dog as a natural model of human aging.”

1.Why do researchers study dogs’ sleep?

A. To help the dogs sleep well

B. To study dogs’ sleeping activity

C. To control dogs’ learning ability

D. To know more about human brains

2.What is the relationship between the number of sleep spindles and dogs’ learning ability?

A. They have nothing to do with each other

B. Dogs with less spindles have better learning ability

C. Dogs with more spindles have better learning ability

D. Dogs’ learning ability is totally decided by spindle number

3.What can we know about old dogs in Paragraph 4?

A. They are easy to play jokes on

B. They can finish tasks one after another

C. They are good at solving new problems

D. Their memories are not so good as before

4.Which is the best title for the text?

A. What we can do to let dogs sleep

B. What we can learn by watching sleeping dogs

C. What the saying “Let Sleeping Dogs Lie” means

D. What is the difference between humans and dogs