Many beautiful birds live in the wild. They are our friends. Do you know how birds keep warm in winter? People used to thinktheykeep warm by shaking and using their feathers as our woolen clothes. Few people would think heat might come from inside birds.

This year, researchers at Lund University in Sweden have found that birds’ blood produces more heat in winter, when it is colder than in autumn. The secret is the energy factories of cells, the mitochondria (线粒体). Many animals have no mitochondria in their red blood cells, but birds do.

“In winter, instead of producing more energy, the mitochondria seem to produce more heat.” says Andreas Nord, the study researcher at Lund University.

Then how do the mitochondria work? The researchers examined different birds on two different seasons: early autumn and late winter. The researchers took bloodsamples (样品) from the birds and got the red blood cells. By using a scientific tool, the researchers then were able to know how much oxygen was spent on producing energy, and how much was spent on creating heat. Finally, they also got the amount of mitochondria in each blood sample.

The results are as follows. The blood samples taken in winter had more mitochondria. Besides, the mitochondria worked harder. However, the work was not to produce more energy. The researchers had no idea that the birds could change their blood as a heating system in this way, so they were surprised.

The birds’ bloods produce more heat in winter! Why? Is cold weather the main reason? The researchers will do more study to find it. Among other things, they will also study whether the food that the birds eat in winter affects the mitochondria.

【小题1】What does the underlined word “they” in Paragraph 1 probably refer to?

A．Birds

B．People

C．Friends

D．Animals

【小题2】Which of the following statements about the mitochondria is TRUE?

A．The mitochondria work much harder in autumn.

B．The mitochondria produce more heat in autumn.

C．Many animals have them in their red blood cells.

D．Birds have the mitochondria to keep warm in winter.

【小题3】Which is the correct order about how the researchers did the study?
①They found how much oxygen was spent.
②They got the red blood cells from the samples.
③They got the amount of mitochondria.
④They took blood samples from the birds.

A．④②③①

B．④②①③

C．④①②③

D．①④②③

【小题4】In which part of a newspaper can we find this passage?

A．Culture.

B．Sports.

C．Science.

D．People.

【小题5】What’s the best title of the passage?

A．The mitochondria are very useful	B．Blood helps birds keep warm in winter
C．We should protect our friends—birds	D．Researchers did a successful study