题目内容：

A decade-long study, also the first major research into air pollution and disease has shown that living near a main road increases the risk of dementia(痴呆). The study of 6.6 million people found that one in 10 dementia deaths in people living within 50 metres of a busy road was due to waste gas and noise. 

Air pollution is already known to contribute to the deaths of around 40,000 people in Britain each year by worsening breathing and heart conditions, while previous research showed emissions (排放物) can cause brain shrinkage. But the new study by Canadian public health scientists is the first to find a link between living close to heavy traffic and the increasing of dementia, a discovery described as "believable" and "impressive" by British experts. 

Dr Hong Chen said. "Our study suggests that busy roads could be a source of environmental stressors that could give rise to the onset of dementia. Population growth and urbanization has placed many people close to heavy traffic, and with widespread exposure to heavy traffic and growing rates of dementia, even a modest effect from near-road exposure could cause a large public health burden.  More research to understanding this link is needed, particularly into the effects of different aspects of traffic, such as air pollutants and noise."

In the new study, the team tracked all adults aged between 20 and 85 living in Ontario for more than a decade from 2001 to 2012. They used postcodes to determine how close people lived to a main road and analyzed medical records to see if they went on to develop dementia, Parkinson's disease or multiple sclerosis(多发性硬化). 

While there was no correlation between living near a road and Parkinson's disease or multiple sclerosis, dementia risk reduced as people lived further from a main road, with a 7 percent higher risk in developing dementia among those living within 50 metres; a 4 percent higher risk at 50-100 metres and a 2 percent higher risk at 101-200 metres. After 200 metres there was no increase. Researchers believe that noise of traffic may also play a role in the raised risk as well as other urban pollution, which is often present near busy roads.

1.What can we know about Canadian's new study?

A. British experts think highly of it.

B. It brings benefits to dementia patients.

C. It shows that air production is very serious.

D. It shows that air pollution can cause brain shrinkage.

2.What Dr Hong Chen said showed that______.

A. people are diagnosed with dementia mainly due to air pollution

B. widespread exposure to traffic will reduce the risk of having dementia

C. the link between living near roads and having dementia was not obvious

D. busy roads could be a source of environmental stressors that caused dementia to increase

3.What does the underlined the word ‘correlation’ mean?

A. Change.    B. Improvement.

C. Association.    D. Secret

4.What can be inferred from the last paragraph?

A. Living near a main road adds to the risk of noise.

B. Living beyond 300 metres of a main road is safe for people.

C. Living within 200 metres of a main road has a lower risk of having dementia.

D. The further people live away from heavy traffic, the smaller the risk of having dementia.