⑴用pH试纸检验溶液，发现溶液呈强酸性；

⑵取部分溶液逐滴加入NaOH溶液，使溶液由酸性变为碱性，无沉淀产生；

⑶取少量⑵中的碱性溶液，滴加Na₂CO₃溶液，有白色沉淀产生。

①根据上述事实确定：该溶液中肯定存在的离子有____；肯定不存在的离子有____；可能存在的离子有____。

②写出（3）中发生反应的离子方程式____。

When I was about 12 years old， I really wanted a new bike！ I 1 my parents my birthday wish，but I knew there was little hope because my family could 2 have that money.
On my birthday my parents told me they had my 3 outside in the back yard. At once I 4 out to the yard. There was my bike， 5 it wasn’t the bike that I thought it would be. This one was pink， old and worn with age. It was so 6！ I thought I 7 my parents’ feelings because I could see the disappointment 8 their faces and I was sure they could see it on mine. I 9 the old bike and rode it， feeling 10 that I had made my parents feel this way. So I put on a smile， rode as fast as I could and didn’t 11.
As time went by， I began to understand my parents gave me 12 much more than just a rusty（生锈的）old bike. They gave me a life lesson about 13. When you give something out of love， it doesn’t matter what it is in fact. What matters is the love that is in it. I like to remember this 14 because giving a gift is not about money. It’s about how much love you can feel from it. Do remember， a gift that 15 two dollars isn’t any less valuable（有价值的）than one that costs one hundred dollars， or even more.

据统计，目前南充市私家车出现井喷式增长：小汽车从5万辆增加到6万辆用了不到12个月时间．汽车排放的尾气（CO,SO₂与NO等物质）将会加重我市空气污染，其治理方法有：