题目内容：

 

LONDON: What could possibly be wrong with planting trees? The advantages are obvious; they  firm the soil, soak up (摄取) extra water and take carbon dioxide (二氧化碳) out of the atmosphere.

However, it now turns out that planting trees could add to global warming.

Tree roots do a great job of keeping soil firmly on the ground and out of the wind’s power. The problem is that some of those dust clouds play an important part in soaking up carbon dioxide.

Huge dust storms blow out over the oceans from dry parts of North Africa and central Asia. Tons of dust are lifted and left as a thin film over the ocean surface. The dust fuels oceanic life.

Dust from China is carried east and left in the Pacific Ocean. If a tree-planting programme there is successful and the dust supply reduced, the net result may be that less carbon dioxide gets locked away in the ocean.

Andy Ridgwell, an environmental scientist from the University of East Anglia, has spent the past few years studying dust and says his work “shows clearly the complexity of the system and the importance of not tinkering(粗劣地修补) with it without understanding the results. For this reason there is the need to focus(集中) on cutting carbon dioxide giving off rather than monkeying (瞎弄) about with the land surface.”

An American scientist, Robert Jackson, has shown that when native grassland areas are invaded(侵入) by trees, carbon is lost from the soil. “We are studying why the soil carbon disappears, but one theory is that trees do a lot more of their growing above ground compared to grasses, so less carbon goes directly into the soil from trees, ” says Jackson.

In wet areas of the world, the gain from trees absorbing carbon dioxide above ground seems to be outweighed(超过) by the loss of carbon from the soil below ground. Countries that plan to combat global warming by planting trees may have to think again.

Solutions(解决办法) to environmental problems are often more complex than they first appear, and understanding the Earth’s climate is a very great challenge.

1.People usually hold the opinion that       .

    A．huge dust storms can destroy carbon dioxide

    B．huge dust storms can destroy the oceans on the earth

    C．huge dust storms can’t do anything beneficial for man

    D．planting trees is the only way to control huge dust storms

2.Andy Ridgwell, the environmental scientist, believes that       .

    A．dust plays a more important part than trees

    B．trees shouldn’t have been planted in dry places

    C．carbon dioxide is harmful to everything on the earth

    D．environmental problems are more complex than expected

3.Robert Jackson’s experiment proves that         .

    A．grassland areas should be covered by forests

    B．trees hold more carbon than grass

    C．carbon can turn grass into dust

    D．less carbon can make trees grow faster

4.The underlined word “combat” in the last paragraph means      .

    A．learn about  B．fight against    C．live with    D．give up