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“土电话”：用细线连接贴着纸片的两节竹筒并张紧细线，能实现10m远距离间通话，如图所示．这说明______．

答案

“土电话”之间的声音是通过细线传播的，说明固体能够传声．

故答案为：固体能够传声．

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从-7，-1，2三个数中任取一个，作为一次函数y=kx+b的k值，则所得一次函数中y随x的增大而增大的概率是______．
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单项选择题

Since life began eons ago, thousands of creatures have come and gone. Some, such as the dinosaurs, became extinct due to naturally changing ecologic conditions. More recent threats to life forms are humans and their activities. Man has drained marshes, burned prairies, dammed and diverted rivers. Some of the more recent casualties of man’’s expansion have been the dodo, great auk, passenger pigeon, Irish elk, and Steller’’s sea cow. Sadly, we can no longer attribute the increasing decline in our wild animals and plant species to "natural" processes. Many species are dying out because of exploitation, habitat alteration or destruction, pollution, or the introduction of new species of plants and animals to an area. As mandated by Congress, protecting endangered species, and restoring them to the point where their existence is no longer jeopardized, is the primary objective of the U.S. Fish and Wildlife Service’’s Endangered Species Program.

Which of the following is NOT a cause of increasing decline of wild animal population

A．Exploitation.

B．Pollution.

C．Habitat alteration.

D．Congressional law.
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