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【单选题】
The science of wildlife management is actually quite new. It is the third major phase of the original conservation movement. The first phase involved the preservation of wildlife through laws and hunting regulations. This phase was a reaction against the terrible destruction of many wild creatures. The second phase involved the control of certain birds and animals that were preying on other wildlife and causing their decline. However, the first two phases of the conservation movement had serious limitations. The new laws al lowed certain animals to increase so much that they actually 'ate up' their habitat. Many of them starved to death because the land simply could not provide for them all. Something had to be done. This is how careful wildlife management came into being. One of the chief concerns of wildlife management is the protection and improvement of the natural habitat so that animals have enough food and water to survive. Wildlife management involves care of the soil to produce good vegetation. It involves care of plants and bushes, not only as a source of food, but also as protection. Animals needs cover to hide from their natural enemies and to raise their offspring safely. Just as crops are harvested, wildlife too must sometimes be 'harvested'. By allowing limited hunting and fishing, good management can control certain species that threaten to overpopulate their habitat. Another major part of the wildlife management is the increasing of certain species by artificial means. Some creatures, like the whooping crane, were brought back from the edge of extinction in this way. In order to save these species, members of wildlife teams have reared the young in the safety of research stations. The passage is mainly about ______.
A.
the history of the wildlife conservation movement
B.
the preservation of wildlife through laws
C.
wildlife management as a new approach
D.
protection and improvement of the habitat of animals
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皮皮学刷刷变学霸
举一反三
【单选题】已知M=cos15°sin15°,N=cos 2 15°-sin 2 15°,由如程序框图输出的S= [     ]
A.
0
B.
C.
1
【单选题】cos60°cos15° + sin60°sin15° 等于 ( )
A.
cos30°
B.
sin60°
C.
cos45°
D.
cos60°
【简答题】数控机床按刀具运动轨迹可以分为三类,分别是:
【单选题】化简cos15°cos45°-cos75°sin45°的值为(  )
A.
1 2
B.
3 2
C.
- 1 2
D.
- 3 2
【单选题】关闭离心泵时应该先关闭出口阀,其原因是()。
A.
以防因底阀不严物料会倒流
B.
以防发生气蚀现象
C.
以防使泵倒转而可能打坏叶轮
【单选题】关闭离心泵时应该先关闭出口阀,其原因是()。
A.
以防因底阀不严物料会倒流
B.
以防发生气蚀现象
C.
以防使泵倒转而可能打坏叶轮
D.
以防启动电流过大烧坏电机
【单选题】cos15°cos105° + sin15°sin105° = ( )
A.
B.
C.
0
D.
1
【简答题】数控机床按运动轨迹可分为三类 ()()()
【单选题】离心泵启动时应该关闭出口阀,其原因是:
A.
若不关闭出口阀,则开泵后抽不上水来。
B.
若不关闭出口阀,则会发生气缚。
C.
若不关闭出口阀,则会使电机启动电流过大。
D.
若不关闭出口阀,则会发生气蚀。
【单选题】数控机床的种类按运动轨迹划分则可分为()
A.
二轴控制、三轴控制和连续控制
B.
点位控制、直线控制和连续控制
C.
二轴控制、三轴控制和多轴控制
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