问题
单项选择题
The step of a pilot ladder which prevents the ladder from twisting is the（）.
A.proof bar
B.shifting bar
C.long bar
D.spreader
答案
参考答案：D
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The step of a pilot ladder which prevents the ladder from twisting is the（）.
A.proof bar
B.shifting bar
C.long bar
D.spreader
参考答案：D