1 . They give us paper and fuel, as well as vital ecological set-vices—like cleaning the air, storing carbon and providing home. We’re talking about trees, of course.

But human changes to the environment appear to be causing great changes to trees around the world. In a new study, scientists reviewed global research on trends in tree seedlings (幼苗)，growth, and death. They combined those data with an analysis deforestation (森林采伐). And they found worldwide, older trees are dying at a higher rate than in the past, due to reasons like rising air temperature, wildfires, drought(干旱) and pathogens (病菌).

“ And most of the drivers of that decrease in large, old trees are increasing themselves, such as temperature going up, droughts are more severe, wildfires, windstorms, and deforestation are all—although variable across the globe—they’re generally increasing. And so both the loss has already occurred, but we expect more continued loss of big, old trees,” said Nate McDowell, an earth scientist at Pacific Northwest National Lab, who was one of the study’s authors.

“So if we have an increasing rate of death, particularly of the larger, older trees, what’s left are the younger trees. So that’s why on average, through the loss of bigger, older trees, our forests are becoming younger and shorter. This trend is a problem, because old trees are vitally important.”

“The increase in death does limit the carbon storage of an ecosystem, and can force the system to become a carbon source to the atmosphere. The second reason is from a biodiversity viewpoint—old trees tend to house a higher biodiversity. And the third reason is linked with beauty: as a society we care about these trees. We have national parks named after these big trees.” Nate McDowell added.

1. What’s the purpose of the author in writing the passage?

A．To warn us to care about old trees.

B．To call on us to plant more trees.

C．To tell us why old trees are dying out.

D．To prove forests are becoming smaller.

2. Which of the following does Nate McDowell think is a problem?

A．There’ll be a larger number of older trees.

B．Older trees will disappear in the world.

C．Young trees will be cut down by people.

D．Trees will become younger and shorter.

3. Why are old trees important?

A．They are beautiful.

B．They can shelter a variety of wildlife.

C．National parks have access to them.

D．They limit the carbon storage of an ecosystem.

4. What may be the best title for the text?

A．Temperature Destroys Forests.

B．Forests Gets Younger and Shorter

C．The Reasons of the Loss of Old Trees

D．The Driver of the Decrease of Old Trees