假定英语课上老师要求同桌之间交换修改作文,请你修改你同桌写的以下作文。文中共有10处语言错误,每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。

增加：在缺词处加一个漏字符号(∧),并在其下面写出该加的词。

删除：把多余的词用斜线(﹨)划掉。

修改：在错的词下划一横线,并在该词下面写出修改后的词。

注意：1. 每处错误及其修改均仅限一词；2. 只允许修改10处,多者(从第11处起)不计分。

    Thank you for your letter. Due to the fact that I am on business in another city, I couldn't reply your letter directly after I received it. Now I am writing to tell you that my city has done to reduce traffic jams in the last few years.

    First of all, four subways and some expressways has been built in my city to ease the heavy traffic. Second, it is public transportation which makes it convenient for people to take buses. Third, the parking fee is raised in the downtown, it helps to reduce the number of cars come in and out.

    Now there are more buses and few cars in my city. The traffic is flowing smooth during the rush hour. Can you tell me something about the traffic in your city? Expecting for your reply!

我们平时喝的瓶装矿泉水，每瓶净装水550g，则：

（1）矿泉水瓶的容积至少要多少ml？

（2）若用该矿泉水瓶来装家庭常用的酱油，装满后至少能装多少g的酱油？（ρ_矿泉水=1.0×10³kg/m³，ρ_酱油=1.1×10³kg/m³）

下列现象中物体动能和重力势能都发生变化的是（ ）

“PM2.5”指数是空气中可入肺颗粒物的含量，是空气质量的指标之一．下表为A市1﹣12月“PM2.5月平均指数”（单位：微克/立方米）