题目

已知碳酸氢钠受热易分解，而碳酸钠热稳定性好。取碳酸氢钠和碳酸钠的混合物10.0g，加热到固体质量不再改变为止，得剩余固体6.9g．下列说法正确的是 A．剩余固体为混合物  B．反应后生成CO2的质量为3.1g C．原混合物中NaHCO3和Na2CO3质量比为21:29    D．反应前后的固体分别与相同浓度稀盐酸恰好完全反应所需盐酸质量相同— My parents have been to Hongkong. — Really? When ______ there? A. have they gone B. have they been C. did they go D. will they go