阅读理解。

Scientists in the United States say plant life has increased on Earth in the past twenty years and that in every

area of plant growth the increase is the result of weather conditions.

Eight scientists from across the United States did the study. The space agency NASA and the Department

of Energy paid for it. The findings were published in the magazine Science.

The researchers spent one and a half years examining weather satellite information. The information was

recorded from 1982 to 1999.That period was one of the warmest on record. Researchers found that rainfall

generally increased during that time.

The satellites measured the number of leaves on plants and the amount of sunlight taken in. The scientists

used that information to estimate what is called net primary production. This is total amount of carbon stored

in land plants.

The scientists report a 6% increase in stored carbon since 1982.They say gains were high in equatorial

areas, especially around the Amazon River in South America. The area alone had a 1% increase in the net

primary production.

Ramakrishna Nemani of the University of Montana in Missoula headed the study. He says reduced cloud

cover led to growth in Amazon area. He also says the lack of clouds allowed more sunlight to get through.

More sunlight meant increases in photosynthesis (光合作用).That is the process by which plants use energy

from sunlight to produce the chemicals they need to grow.

Northern Canada, the north-central United States and northern Europe were second in increased plant

growth.Ramakrishna Nemani says a rise in temperature helped plants there.

All together, the report says 25% of areas of plant life on Earth experienced increases. But the scientists

also note increase in the number of people on Earth and carbon dioxide levels in the atmosphere. Ranga Myneni

of Boston University in Massachusetts, another study scientist says humans use about half the net primary

production on Earth. And he notes that the world population grew by 36% during the period of time studied.

1. Which of the following is in charge of the study?

A. The space agency NASA of the US.

B. The Department of Energy of the US.

C. Ramakrishna Nemani in Missoula.

D. Ranga Myneni in Massachusetts.

2. What's the main cause of the plant growth put forward by the study?

A. Growth in population.

B. Regional features.

C. Seasonal variation.

D. Weather conditions

3. Why do scientists believe that reduced cloud cover has led to the plant growth in the Amazon area?

A. Because plants could take in more sunlight.

B. Because plants could get more rainfall.

C. Because plants could enjoy cooler air.

D. Because plants suffer less from natural disasters.

4. Which of the following descriptions about the years from 1982 to 1999 is TRUE?

A. It was the warmest on record.

B. Rainfall decreased little by little.

C. World population grew by 25%.

D. Stored carbon increased by 6%.