题目

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。Changing People’s Bad Impression On UsSome of us have made bad first impressions in front of people we wanted to become good friends with.First impressions are important because they form the foundation on which all future thoughts about someone will be based.【1】However,there are actions you can take to change people's bad impression of you.●Apologize immediately.A sincere apology can go a long way because you will prove to everyone that you value their thoughts ab某无色气体可能是H2、CO、CO2、NH3、HCl、N2中的若干种混合而成。将此气体依次通过实验装置：A→B干燥C→D，实验现象如下表所示。所盛试剂实验现象A澄清石灰水无白色沉淀B氢氧化钡溶液有白色沉淀生成C氧化铜粉末（加热）粉末由黑变红D无水硫酸铜粉末无明显现象根据以上实验现象，试推测：此混合气体中一定含有　　　；一定不含有　　　　；可能有　　　　。??