Question

    City trees grow faster and die younger than trees in rural forestry, a new study finds. Over their lifetimes,then, urban trees will likely absorb less CO2 from the air thah forest trees.

As we all know, the earth would be freezing or burning hot without C02. However, CO2 is a greenhouse gas, meaning it traps energy from the sun as/heat. That makes temperatures near the ground rise. Human activities, especially the widespread burning-of fossil(化石）fuels，have been sending extra greenhouse gases into the air. This has led to a rise in average temperatures across the globe.

Studies had shown forests readily absorb C02，but there hadn’t been much data on whether city trees grow， die and absorb CO2 at the same rate as forest trees do. So some researchers decided to find out.

To figure out how quickly trees were growing, researchers tracked their diameters (the width of their trunks) between 2005 and 2014. A tree’s diameter increases as it grows, just as a person’s waist size increases as they gain weight. About half the weight of a tree is carbon, research has shown. Most of the rest is water. Over the nine years’ tracking, the researchers found city trees absorbed four times as much carbon from the air as forest trees. However, they were twice as likely to die. So over the lifetime of each type of tree, forest trees actually absorbed more C02.

City trees grew faster because they had less competition for light from their neighbors. In a forest，trees tend to grow close together，shading their neighbors. Street trees also benefit from higher levels of nitrogen (氮）in rainwater. Nitrogen helps plants grow. Waste gases from gas-burning cars also contain nitrogen, thus enriching city air with nitrogen. Later, rainwater may wash much of it to the ground. Some street trees may also have better access to water than trees in the country because the underground water pipes can leak.

1.What can he known about CO2 from paragraph 2?

A.It is one of the side effects of greenhouses.

B.It greatly accelerates the process of global warming.

C.It results from the widespread burning of fossil fuels.

D.It prevents the earth from becoming unsuitable to live on.

2.Why did researchers track the diameters of trees?

A.To know about their growth rates.

B.To find out how much they weigh.

C.To check whether they were healthy.

D.To assess the carbon amounts in them.

3.What advantage do city trees have over forest trees?

A.They are more likely to access growth promoters.

B.They can enjoy more water coming from the air.

C.They can enjoy more shade from neighbors.

D.They are better at competing for light.

4.What will probably be talked about if the passage is continued?

A.How urban trees can live longer.

B.Why city living makes trees die young.

C.How trees respond to dry soil conditions.

D.Why faster-growing trees absorb more C02.

Answer

1.D

2.A

3.A

4.B

【解析】

这是一篇说明文。一项新的研究发现：与长在森林中的树木相比，城市里的树木长得更快，但死得更早。

1.推理判断题。根据第二段中the earth would be freezing or burning hot without CO2.可知，如果没有二氧化碳，地球将会极冷或极热。可以推断，二氧化碳可以防止地球变得不适合居住。故选D项。

2.细节理解题。根据第四段中To figure on how quickly trees were growing, researchers tracked their diameters.可知，研究人员监测树木的直径是为了了解树木的生长速度。故选A项。

3.细节理解题。根据最后一段内容Street trees also benefit from higher levels of nitrogen (氮）in rainwater. Nitrogen helps plants grow. Waste gases from gas-burning cars also contain nitrogen, thus enriching city air with nitrogen. Later, rainwater may wash much of it to the ground.可知，与生长在森林中的树木相比，城市里的树木长得更快是因为它们无需与邻近的树木争夺光照，也能得到更多的氮量，还更容易得到水。光、氮和水都可以促进树木的生长。由此可以推断，城市里的树木比森林中的树木更可能获得生长促进剂。故选A项。

4.推理判断题。文章首句就提到了一项新的研究结果：城市里的树木比森林中的树木长得更快，但死得更早；文章第三段说到“以前有研究表明森林会吸收二氧化碳，但是城市里的树木的生长、死亡和吸收二氧化碳的速度是否跟森林中的树木一样，这方面的数据不多。因此一些研究人员决定弄清楚”；文章第四段再次介绍了他们的研究发现：城市里的树木比森林中的树木长得更快，但死得更早；文章最后一段介绍了城市里的树木比森林中的树木生长得更快的几个原因。由此可以推断，文章接下来很可能就要介绍城市里的树木死得更早的原因。故选B项。