你的英语属于chin-English,很多语句是按照中文的说法写的.比如：
Let me introduce you to a variety of pollution problems.你可以改为：There are variety of pollution problems as we know,the one I reffers is air pollution,………… the second is …… the last one is
结尾部分作为演讲来说过于突兀,但pollution这个问题过大,试试用问题结尾.