3．In a recent study，researchers at Germany's Technical University of Munich （TUM） find that trees in cities can grow up 25% faster than their country cousins.This is believed to be a direct result of the heat island effect，which is a situation where the temperature of the city is higher than the nearby rural areas.It's mostly caused by the fact that buildings，roads，and many other things in the city take in a lot of sunlight and send out the sun's heat more than natural landscapes such as forests and water bodies.A secondary cause is waste heat produced by heavy uses of energy.
For the study，TUM researchers studied 1，400 trees in 10 cities around the world，which were found in both city centers and nearby rural areas.Based on tree ring study，researchers found that city trees are growing faster than their rural cousins.But before the 1960s，both city and rural trees grew at about the same speed."We can show that city trees of the same age are generally larger than rural trees because they grow faster.While the difference is about a quarter at the age of 50，it is still just under 20% at a hundred years of age，" lead author Hanz Pretzch says.
Researchers from TUM also found that in some cities，higher-than-normal temperatures have led to growing seasons that are more than eight days longer than the norm.This sounds like a good thing.But while fast -growing city trees are busy taking in CO
2 and providing relief from the heat，they're also aging and dying at a faster speed than rural trees.As a result，these trees need to be replaced and replanted more frequently.
Considering the valuable "ecosystem services" that city trees provide，planning and management should follow to make a change with today's tree growth speed.Pretzch and his team set out to perform the study largely in response to United Nation's report that the world's cities will experience population growth of more than 60% by 2030.And with such fast growth comes a great need for city trees that make these cities better places to live in.
（1）What does the first paragraph mainly tell us？
A．Cities need more trees to reduce the temperatures.
B．Humans lead to trees growing faster in cities.
C．Trees need scientific planting in rural areas.
D．Greenhouse effect is too serious in cities.
（2）What can we learn from the findings of the research？
A．Rural trees live twice longer than city trees.
B．City trees live for about 100 years at most.
C．Rural trees live much longer now than in the 1960s.
D．City trees grow faster at early years.
（3）What is the result of city trees growing faster？
A．Cities suffer more easily from natural disasters.
B．The temperatures in cities will fall greatly.
C．City trees have a shorter life circle.
D．More people move to rural areas.
（4）Which of the following might be the best title for the text？
A．Taking better care of urban trees
B．Planting more trees in urban areas
C．More researches to be done on urban trees
D．Urban trees growing faster than rural trees
