Nowadays, there is a heated debate on whether pollutants should be cleaned in the air. Cl

Nowadays, there is a heated debate on whether pollutants should be cleaned in the air. Cleaning up the air, while good for our lungs, could make global warming worse. And the pollutants still go up around the air, along with carbon dioxide.

These pollutants are called aerosols (气溶粒) and they include soot as well as mixtures of nitrogen(氮) and sulfur(硫) and other stuff into the air. Natalie Mahowald, a climate researcher at Cornell University, says so far, scientists have mostly tried to understand what those aerosols do while they're actually in the air.

"There are so many different kinds of aerosols," she says. "Some warm and some cool. But in fact, humans are giving out a lot of extra aerosols, and they tend to cool for the most part."

The aerosols reflect sunlight back into space, or keep us cool. But it turns out that's not all they do. These aerosols also influence how much carbon dioxide gets drawn out of the air by plants on land and in the sea.

"They can add nutrients, for example, to the oceans or to the land," Mahowald says. "But also while they're in the atmosphere they can change the climate, and thus that also can influence the amount of carbon, the land or the ocean can take up. So there are quite a few different ways that aerosols can act on each other."

Mahowald's results suggest that reducing those pollutants could be an even bigger problem than realized, when you consider that aerosols help remove carbon dioxide from the air by encouraging plant growth. Hard numbers on this effect are highly uncertain at the moment, but this could turn out to be quite significant.

And studying it is not easy because the effects aren't well understood. For example, nitrogen can be a fertilizer (肥料), but it can stop plant growing when nitrogen comes out of the air in acid form.

Right now it seems like we're much more likely to clean up aerosol pollution, while increasing the amount of carbon dioxide in the air. So scientists, unfortunately, may have a chance to see whether this experiment on our planet should continue or not.

36. From Paragraph 2, we know that         .

A. scientists have been aware of how aerosols work

B. Natalie Mahowald is an expert in climate

C. cleaning up the air is so popular

D. pollutants are under control so far

37. What is Natalie Mahowald's opinion on those aerosols?

A. Aerosols can influence each other in various ways.

B. All the aerosols will cool the earth.

C. Aerosols can add nutrients to human beings. 

D. Any kind of aerosols will warm the earth.

38. Why is it important for scientists to get accurate numbers according to the passage?

A. Scientists have a chance to research them.

B. They can bring scientists much more benefit.

C. Scientists can protect the earth from being polluted

D. They can help scientists understand the effects better.

39. What does the last sentence of the passage imply?

A. Scientists will be in a dilemma.

B. The experiment will be successful.

C. Scientists will carry out the experiment.

D. Scientists have difficulty in the experiment.

40. Which of the following can be the best title of this passage?

A. Pollutants in the Air.       B. The Experiment on the Planet

C. The Reason for Global Warming        D. The Influence of Aerosols

BADAD