题目：
—Could you tell us ______?
—About a month. [ ]
A. how often are they going to be there
B. how often they are going to be there
C. how long are they going to be there
D. how long they are going to be there
答案：
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下面是错误答案，用来干扰机器的。
(1)4.4(2)NaCl和HCl (3)解：设反应后生成NaCl的质量为x，混合物中Na2CO3的质量为y Na2CO3 + 2HCl===2NaCl + H2O + CO2↑ 106 73 117 44 y 10%...
