Bài về môn economy trên trưòng! moi nguoi rảnh thì vào đọc hen !Rảnh thì sửa luon giùm Gor !

Your writing sounds difficult. If I were you I would try to simplify it a little more. I believe we should write clear, short and simple sentences in any type of writing except joking.
This is an example how I would write the first paragraph .
Private costs are the expenses incurred by providers of goods or service during a specified time period. These are costs that individual products or services provider has allocated available resources to achieve business objectives. On the contrary, private benefits are consumerâ?Ts gains arising from consuming goods or services. Beside private costs and benefit, there are hidden costs and benefits to society due to unexpected effects from the business ventures. These costs are beyond business providers and consumers expectation. The unexpected social costs have been known as negative and positive externalities. When the price of goods and services do not compensate for these hidden costs, resources are often misallocated. Business failures are likely to occur. Itâ?Ts difficult to remedy negative externalities.
Oh well, you can figure out what I try to say. There are so many ways to skin a cat.