问题
单项选择题
A tackle by which the outer end of a boom is raised and lowered is the topping（）.
A.Boom
B.Lift
C.Raise
D.Tackle
答案
参考答案：B
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A tackle by which the outer end of a boom is raised and lowered is the topping（）.
A.Boom
B.Lift
C.Raise
D.Tackle
参考答案：B
