在实际业务中，如买方未按合同规定时间开立信用证，卖方必须进行催证工作()。
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牙釉质粘接剂可分为两类，即_______和_______。
Weaker bonds to dentin are caused by one of the reasons that()
A. dentin contains more mineralized tooth structure than enamel
B. dentin contains more water than enamel
C. the smear layer makes wetting by adhesive more effective
D. fluid m the dentin tubulesreduces the stability of the composite resin to dentin bond
解决钢材腐蚀问题通常采用()方法。
A. 合金防腐、表面包层防腐
B. 不接触空气
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