生态系统中必须有的生物成分是生产者和消费者。 [ ]
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The author of this passage is most probably________.
A. a historian
B. a doctor
C. a nutritionist
D. an environmentalist
The wallet which the writer found______.
A. was empty
B. had some money in it
C. had a few coins and a photograph in it
D. had an old photograph in it
在生态因子中，对生物生存和繁殖起关键性作用的主导因子。 [ ]
A. 正确
B. 错误
农业生态系统是一种耗散结构。 [ ]
A. 正确
B. 错误
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