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     Trees in cities "live fast but die young" compared to forests in the countryside， warns a new study．

     Researchers found that trees in cities die younger than ones in the countryside because of the higher levels of CO₂． City﹣living trees suffer（遭受） a loss of carbon storage（碳储量）． That means trees produce less energy from the air．

     Now researchers say more must be done to deal with the situation． Ian Smith， a PhD student of Boston University in the United States， said， "Cities are in the important position in fighting against rising temperatures and increasing CO₂．"． "We find that tree planting alone may not be enough to keep and increase city canopy cover（树冠覆盖率）． Because of the age and size of the present canopy， efforts to improve and protect tree health are badly needed for increasing city tree cover and canopy cover．"

     The research team used a model to watch changes among street trees for several planting and management methods． Researchers also used the model to watch tree growth， death and planting rates（率）both among trees in Boston city and forests in the countryside in Massachusetts．

     It was discovered that rates of carbon cycling and growth rates among city trees were nearly four times faster than those in the countryside． However， loss of carbon storage and death rates are also higher， especially death rates are more than double higher than those in countryside forests．

     The study， published in PLOS ONE， has reminded scientists to encourage communities to do more to plant and protect trees． It is important to increase city canopy cover and carbon storage．

    Researchers say planting and protecting will be needed to make sure cities can develop healthily， but more needs to be done to have a better understanding of city trees ﹣﹣﹣which may be different from countryside forests．

（1）According to the passage， which of the following is TRUE？　　

A． The more carbon storage loses， the more energy the trees produce from the air．

B． The higher the levels of CO₂ are， the harder it will be for the plants to survive．

C． If we plant enough trees， we are sure to increase city canopy cover．

D． Cities do better in fighting against rising temperatures and increasing CO₂．

（2）Paragraph 4 mainly tells us　　．

A． the results of the study

B． the discoveries from the researchers

C． the methods of the study

D． the suggestions from the researchers

（3）What does" those" in Paragraph 5 refer to？　　

A． Death rates．

B． Rates of carbon cycling．

C． Growth rates．

D． Loss of carbon storage．

（4）The writer's main purpose of writing the passage is　　．

A． to teach us how to improve and protect tree health

B． to warn us that trees in cities live fast but die young

C． to let us have a better understanding of city trees

D． to tell us to take action to increase city canopy cover

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