Here is another example of a simple error of omission that could have been caught if the student had read the essay aloud or given it to a friend to read. The word "of" should be between "calculation" and "the." That one small error makes the entire sentence awkward and confusing. If the instructor has to reread the sentence to try to understand its meaning, the flow of the essay is interrupted. If this happens often enough in the essay, it gives an overall bad impression on what otherwise might be a very good paper in terms of research.
From the point of countries, politicians will perceive the ongoing situation as a wake-up call with regard to lower birth rates, more demands on houses, and more energy consumption. Firstly, more single households mean more single persons, and the population will shrink in the wake of falling number of married couples. Secondly, more houses are required to fulfill the need of individuals, which cause cities even more densely populated. London is a famous example; the number of houses has been stimulated by 48% over the past five years, and 80% of them are for singles. Finally, the consumption of electricity and gas will soar when more people choose to live on their own, and it will further pose a threat to our livelihood.