在敞开式循环水冷却水系统无论是新系统还是老系统，在开车正常投药之前都要进行系统（）和（）工作。
参考答案：清洗；预膜
汉译英：“承兑交单；付款交单；货到即付”，正确的翻译为：（）
A．document against acceptance; document against payment; payment against arrival
B．document against payment; document against acceptance; payment against arrival
C．document against acceptance; payment against arrival; document against payment
D．payment against arrival; document against payment; document against acceptance
将4.4g二氧化碳气体通入200g氢氧化钠溶液中，恰好完全反应．请通过计算回答下列问题：
（1）反应后所得溶液的质量；
（2）反应后所得溶液的质量分数；
（3）所得溶液中钠元素的质量分数．
