Builders have known for many years that white roofs reflect(反射) sunlight and lower the cost of air conditioning (空调设备). But now scientists say they have found a new advantage: slowing global warming.
Hashem Akbari believes that whitening 100 of the world’s largest cities could make the influence of the expected emissions (排放物) smaller over the next ten years.
White buildings and surfaces reflect far more sunlight than dark ones. Reflected sunlight does not increase the greenhouse effect (温室效应), unlike the heat energy sent out by dark surfaces heated by the sun.
Dr Akbari, of the Lawrence Berkeley National Laboratory, California, also argues that If built-up areas were made white, less heat would stay within them, allowing people to use their air conditioners less, which use a lot of power.
Dr Akbari has found out that making 100 of the largest cities white would increase the sunlight reflected by Earth by 0.03%. He believes it would cancel out (抵消) the warming caused by 44 billion tons of carbon (碳) emissions.
“Roofs are going to have to be changed one by one and to make that effort at a very local level, we need to have an organization to make it happen,”says Dr Akbari.
He argues that while the action would not solve the problem of climate change. it would slow it.
“We can give the environment time to breathe,” he says. “I just don’t see a disadvantage of this idea. It gives everybody advantages and you don’t have to make hard efforts to make it happen. ”
Akbari and his partners say they will try to persuade the United Nations to organize big cities to change the materials of their roofs.
How do white roofs slow down global warming?

A．They reflect sunlight, which makes people use no air conditioner.

B．They reflect sunlight, which doesn’t increase the greenhouse effect.

C．They keep the heat energy within them.

D．They send out no carbon emissions.

We know from Dr Akbari that he        .

A．has changed some roofs into white ones

B．doesn’t use air conditioners himself

C．has built an organization to make cities white

D．believes his idea will help slow the climate change

What do Akbari and his partners want to do?
A. They hope the UN will put their idea into action.
B. They want to become members of the UN.
C They want to change the materials of their own roofs.
D. They want to teach people how to change roofs
The passags is written mainly to        .

A．persuade people to paint their roofs white

B．introduce environment friendly paint

C．show white roofs do good to the environment

D．discuss how to slow down global warming