3．"How many of us as children have stared up at a church-like top of a giant tree and climbed it in wonder，which is a really special part of our lives？" asks Bill Laurance，a tropical ecologist at James Cook University. "The leaves of big trees in forests are spreading out in all directions.We're faced with organisms that have evolved for long periods of ecological stability. "
"There's a lot to discuss on the issue，" says David Lindenmayer，a conservation ecologist at the Australian National University. "Climate change will mean that，in some forests，big trees won't reach the same sizes they used to." The effects of climate change，including long droughts，more invasive species and so on increase the simple physical challenges that big trees face in pulling water from their roots to their leaves and withstanding windstorms.
Lindenmayer and Laurance define "large，old trees" as the largest five percent mature trees within a species.The flexible definition means that in some forests，the large，old trees might be only 20 meters tall and 100 years old.
These large，old trees control the surrounding plant communities，affect water and nutrient distribution，and provide food and shelter for wildlife. "They're really the breadbaskets of the forest，" says Laurance， "This is a very environmentally and ecologically important group of organisms，and they need special care and handling.Determining the distribution and habitat requirements for large，old trees in the landscape is the first step towards ensuring their survival. "We have to ensure that what we're thinking is long-term，to match the way these trees have existed for hundreds or even thousands of years，" says Laurance. "It's going to be a real challenge to keep some places where there is still wildlife and the big church-like trees that we all really care about. "
（1）How does the author lead in the topic of the text？
A．By definition.
B．By quoting someone's words.
C．By comparison.
D．By drawing some conclusions.
（2）What can we learn about big trees from paragraph 2？
A．They easily pull water from their roots.
B．They have become shorter but thicker.
C．They are affected by various factors.
D．They grow taller because of climate change.
（3）Which of the following does Laurance want to express in the last paragraph？
A．It is necessary to take good care of big trees.
B．The plants around control trees' survival.
C．Big trees mainly depend on wildlife for survival.
D．Planting big trees is the first step in forest protection.
（4）What can be the best title for the text？
A．Fight Against Climate Change
B．Keep Ecological Stability
C．Deal With Forest Organisms
D．Protect Forest Giants
