B vitamins（維生素）may offer some protection against the effect of air pollution,a new study suggests.

The scientists say the effect is real but stress the limitations of their work.Follow-up studies are urgently needed, they say,in heavily polluted cities like Mexico.

According to the World Health Organization (WHO),over 90% of the world's population live in heavily-polluted areas.The one of the pollutants that is considered the most dangerous is very fine particulate matter, referred to as PM2.5.At around 1/30 the width of a human hair,PM2.5 can go deep into the human lung and contribute to lung and heart health problems in the young and old.

Scientists have long suspected that PM2.5 causes what are termed epigenetic（表觀遺傳）changes in our cells that can damage our health.Now in this new human trial,an international team of scientists wanted to see if exposure to concentrations of PM2.5 could be mitigated by daily B vitamins.

Ten volunteers were tested initially exposed to clean air and their basic responses were measured.The same volunteers were later tested with large doses（劑量）of B vitamins while exposed to air containing high levels of PM2.5.The researchers found that a four-week B vitamin intake limited the PM2.5 effect by between 28-76% at ten gene locations.They found a similar reduction in effect on the mitochondrial DNA,the parts of cells that produce energy.

However,the researchers caution that their study,while observing a real effect,has limitations.As well as the small number of participants,there was little information on the size of the B vitamin dose that caused the response.

1.What is the main idea of the text?

A. B vitamins may fight against PM2.5.

B. PM2.5 can lead to epigenetic changes.

C. Further studies should be done on PM2.5.

D. Exposure to PM2.5 is more and more serious.

2.Which can replace the underlined word "mitigated" in Paragraph 4?

A. measured B. ignored

C. reduced D. observed

3.How many limitations does the text mention about the new study?

A. 2. B. 3.

C. 4. D. 5.

4.How does the writer of the text like the new study?

A. He believes it deeply. B. He criticizes it strongly.

C. He thinks it needs testing again. D. He shows no opinion about it.

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