题目内容：

    Air travel is growing around the globe, and so is its contribution to climate change. The climate cost of flying has drawn more public attention in recent years, even leading to“ flight shame” in some places, especially for local or avoidable flights.

And while a decline in air travel would help with climate change，flight shame can also be added by other ways that make air travel more environmentally friendly. That includes switching to cleaner，renewable fuel , but as a new study indicates , there's also another, less obvious option: flying at lower altitudes.

In a new study, researchers used computers to predict how adjusting aircraft altitudes might reduce the number of contrails(尾迹)，which we see as white lines across the sky containing black carbon particles (颗粒)，thus reducing their warming effect. The study found that aircraft would only need to adjust their altitudes by about 2 ,000 feet, and since some flights have a larger climate effect than others , only a small part of flights would need to make any adjustments.

Of course flying at a lower altitude might increase flying time and it also means burning significantly more fuel, and thus giving off more C02, but the benefits of controlling contrails are worth it.

In addition to changing altitudes，better engine technology could also help control contrails, the researchers add, since black carbon particles are produced by incomplete fuel combustion ( 燃烧). With more efficient engines, aircraft could reportedly reduce their contrail by as much as 70%。Combined with slight altitude adjustment for a small part of flights, this could help reduce overall contrail problems by 90%，the study suggests.

This is promising, but more research i still needed, and it may be a while before improvements like these take effect at a significant scale. So, while it's good to know air travel can have a smaller effect on the climate, for now the best way to achieve that is often by simply staying on the ground whenever possible.

1.What might be the effect of“flight shame" ?

A.People will avoid traveling by plane.

B.Airline companies will limit service targets.

C.The cost of air travelling will become higher.

D.People will feel shamed if they haven't taken a plane.

2.Why did the researchers suggest flying at lower altitudes?

A.Planes can travel faster. B.Planes can save more fuel.

C.Planes may give off less C02. D.Planes may have less warming effect.

3.What is mainly talked about in paragraph 5?

A.A way to change altitudes. B.The future of engine technology.

C.An approach to reducing contrails. D.The concept of incomplete combustion.

4.In which section of a website might this text appear?

A.Energy. B.Climate.

C.Finance. D.Safety. .