Using articles (a / an / the) is always a challenge for English language learners. Generally, we use 'a' or 'an' when we talk about something for the first time. After that, we use 'the'. For example: There was a pink car parked in the street. The car had big purple flowers on it. It gets complicated because we also use 'the' for unique things such as 'the President of the United States', or 'the red pen on my desk'. We also use 'the' when the listener/reader knows what we're talking about. For example: You know the languages they speak in the classroom. For these sentences you would use 'a' first, and then when you talk about them again, you use 'the'. Which form should we use for "the group of people", "a group of people", "the increasing number of people" and "an increasing number of people"? An increasing number of working people try to return to campus for further education. The increasing number of people has imposed a heavy burden on the medical system of this city. I don't understand the first part of this sentence: The high educated groud of people is the main force of the development of technology and society. I think you mean 'A highly educated group of people are the main force for the development of technology and society.

Hi M.T, Sentence A: An increasing number of working people (are trying) to return (to) campus for further education. The indefinite article "an" is used to refer to a non-specific noun. Therefore, the sentence is describing a rising trend instead of a very specific number. You may wish to refer to this article which uses "an increasing number" to refer to a trend: http://nhpr.org/post/behind-trend-increasing-number-foreign-students-attending-nh-colleges#stream/0 Sentence B: The increasing number of people has imposed a heavy burden on the medical system of this city. Here, the definite article "The" is referring to the numerical growth in the number of people seeking medical services, and focuses on the number. The (highly) educated (group) of people is the main (driving) force (behind) the development of technology and society. Again, the definite article "The" is referring specifically to a certain specific group of highly educated people. Hope this helps. Cheers, Lance

没毛病，看来你理解了