萃取水中苯胺类化合物时，萃取液脱水使用的无水硫酸钠必须经过（）℃烘4h备用。
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To determine which grades of cargo a tanker is permitted to carry you should（）.
A. refer to the vessel's Certificate of Inspection
B. examine the cargo tanks and fittings
C. ask the terminal supervisor or his representative
D. check the loading order
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