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【单选题】
托盘头的作用有：( )①划45°和90°的线 ②确定圆柱形工件的中心 ③测量工件的高度和深度 ④检测工件表面A.
①②④
B.
①②③
C.
②③④
D.
①③④
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举一反三
【单选题】______ birds use their feathers for flight, some of their feathers are for other purposes.
A.
Once
B.
If
C.
Although
D.
Because
【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.
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