单项选择题
For any given pedestal crane，when the boom is lengthened，the lifting capacity is（）.
A.unchanged B.increased C.eliminated D.decreased
单项选择题 For a given weight of cargo，the stress on the heel block of a cargo boom（）.
单项选择题 Bonding cables are used during cargo transfer to（）.
单项选择题 Backstays are（）.
