The vast majority of rural areas have been rapidly replaced bywith cites, industrial parks, etc (OR and the like)this has causedcausing (OR contributing to)thea dramatic increases in the number of people migrating to cities
--> never use "..." in writing
In today's world, life in countryside, without honking, air pollution,... is considered as the greatest way to live by some people, while some other people claim that living in countryside does have drawbacks.
is this an agree or disagree topic? if so, please add your opinion at the end of the intrduction. btw, the phrase "in the today's world" is not appropriate to be used in this sentence cause it is usually used when you are trying to talk about a worldwide FACT not two different viewpoints of two groups of people.
Open spaces, fresh air and less pollution are some benefits of living in countryside.
This cannot be a topic sentence. In a topic sentence u need to mention a general idea and a precise idea. General idea could be "living in countryside", and precise idea "some advantages". Talking about advantages must be included in the following supporting sentence.
In my opinion, I prefer living in countryside to living in cities despite it'sits disadvantages. Should I get older, I desiremight choose to live in a farm house in a countryside; however, when young, I must try my best in my career, may be in a big city.
Conclusion structure--> reword thesis statement/topic+your opinion if the topic is not agree or disagree; if it is, you need to write your opinion in the introduction+a clincher
hope this helps