Half of the world’s population lives in areas affected by Asian monsoons（季风）, but monsoons are difficult to predict. American researchers have put together a 700-year record of the rainy seasons, which is expected to provide guidance for experts making weather predictions.
Every summer, moist（潮湿的）air masses, known as monsoon, produce large quantities of rainfall in India, East Asia, Indonesia, Northern Australia and East Africa, which are pulled in by a high pressure area over the Indian Ocean and a low pressure area to the south.
According to Edward Cook, a weather expert at Columbia University in New York, the complex nature of the climate systems across Asia makes monsoons hard to predict. In addition, climate records for the area date to 1950, too recent and not detailed enough to be of much use. Therefore, he and a team of researchers spent more than fifteen years travelling across Asia locating trees old enough to provide long-term records. They measured the rings（年轮）or circles, inside the trunks of thousands of ancient trees at more than 300 sites.
Rainfall has a direct link to the growth and width of rings on some kinds of trees. The researchers developed a document—a Monsoon Asia Drought Atlas（地图集）. It shows the effect of monsoons over seven centuries, beginning in the 1300s.
Professor Cook says the tree-ring records show periods of wet and dry conditions. “If the monsoon basically fails or is very weak one year, the trees affected by the monsoon at that location might put on a very narrow ring. But if the monsoon is very strong, the trees affected by that monsoon might put on a wide ring for that year. So, the wide and narrow ring widths of the tree chronology（年表）that we developed in Asia provide us with a measure of monsoon variability. ” Armed with such a sweeping set of data, researchers say they now can begin to refine climate computer models for predicting the behavior of monsoons.
“There has been widespread famine and starvation and human dying in the past in large droughts. And on the other hand, if the monsoon is particularly heavy, it can cause extensive flooding,” said Eugene Wahl, a scientist who is with America’s National Oceanic and Atmospheric Administration’s paleoclimate（古气侯）branch studying weather patterns over the history of the Earth. “So, to get a knowledge of what the regional moisture patterns have been, dryness and wetness over such a long period of time in great detail, I would call it a kind of victory for climate science.”
What’s the passage mainly about?

A．A breakthrough in monsoon prediction.

B．The necessity of weather forecast.

C．The achievements of Edward Cook.

D．The effects of Asian monsoons.

It is difficult for experts to predict Asian monsoons because______.

A．it is hard to keep long-term climate records

B．they are formed under complex climate systems

C．they influence many nations

D．there is heavy rainfall in Asia

What can be inferred from the passage?

A．The trees affected by monsoon grow fast if the monsoon is weak.

B．The Monsoon Asia Drought Atlas has a monsoon record for about 1,300 years.

C．Long and detailed climate records can offer useful information for monsoon research.

D．The rainfall might be low although the monsoon is strong in monsoon-affected areas.

According to Professor Cook, the rings of the trees_________.

A．determine the regional climate

B．have a great influence on the regional climate

C．offer people information about the regional climate

D．reflect all kinds of regional climate information

What do we know about the research according to Eugene Wahl?

A．It will help people prevent droughts and floods.

B．It should include information about human life in the past.

C．It has analysed moisture models worldwide.

D．It is a great achievement in climate science.

Which of the following best describes the tone of this passage?

A．Friendly.	B．Pessimistic.
C．Humorous.	D．Matter-of-fact.