环境空气质量监测中，用碱片―铬酸钡分光光度法测定硫酸盐化速率时，需向样品溶液中加铬酸钡悬浊液，铬酸钡悬浊液在加入前要充分振摇均匀。
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A sufficient amount of chain must be veered when anchoring a vessel to ensure（）.
A. the vessel has enough room to swing while at anchor
B. the anchor flukes bite into the ocean bottom
C. there is a sufficient scope of chain to keep the anchor on the bottom
D. there is more chain out than there is in the chain locker
花果山仙人桥相传因有人在此修道成仙而得名，请叙述仙人桥回文诗。
冷藏车送到装车站后，托运人取消托运，只核收变更手续费。是否正确？为什么？
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