皮皮学，免费搜题
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搜题
【多选题】
起重机的工作速度主要有哪四种( )A.
起升速度
B.
变幅速度
C.
旋转速度
D.
运行速度
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举一反三
【单选题】____birds use their feathers for flight, some of their feathers are for others purposes.
A.
Once
B.
If
C.
Although
D.
baecause
【单选题】During daylight hours, birds ______.
A.
fly aimlessly
B.
rely on landmarks
C.
use sun for guidance
D.
are more likely to get lost
【单选题】According to the author, which is the most feasible way to protect birds?
A.
Use fences to protect all the parks in the world.
B.
Try to protect wild space and nature.
C.
Abandon the economic values that birds can bring.
D.
Rely less on agriculture and return farmlands to forests.