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【多选题】
关于钢管的叙述正确的是( )。A.
根据制作方法，钢管分无缝钢管和焊接钢管
B.
焊接钢管是由优质碳素钢或合金钢制作
C.
无缝钢管有热轧和冷轧两种
D.
焊接钢管按表面处理的不同分为镀锌钢管和不镀锌钢管两种
E.
无缝钢管一般用于作输水管、煤气管、暖气管及结构零件等
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皮皮学刷刷变学霸
举一反三
【单选题】Why does the professor mention fossils?
A.
To describe the evidence Wegener used to develop his theory.
B.
To suggest that Wegener borrowed ideas from earlier scientists.
C.
To explain how Wegener first became interested in geology.
D.
To show why most scientists ridiculed Wegener's theory.
【单选题】Agriculture was a step in human progress ______ which subsequently there was not anything comparable until our own machine age.
A.
to
B.
for
C.
in
D.
from
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