Using “...
in which…” in a sentence is one of the more confusing aspects of writing. It is correctly used in more formal writing. In certain situations not using it will be appropriate for an informal document. To determine whether to use “in which,” you need to consider your writing situation. Does your audience expect strict formal grammar? Is this an informal writing situation? First let’s define what parts of speech the phrase “in which” consists of. “In which” is a combination of a preposition (in) and a relative pronoun (which). You can use “in which” as a precise way to introduce a relative clause after a noun that refers to a place or to a time. For example instead of saying
In my laboratory there is a blue cabinet where old equipment is stored.
You can say
In my laboratory there is a blue cabinet in which old equipment is stored. Or instead of saying
The man sat at the computer where his old accounting files were stored. (place)
It was a time when the old were revered as sages. (time)You can say
The man sat at the computer in which his old accounting files were stored.
It was a time in which the old were revered as sages. (time)
Use “in which” to avoid ending a sentence with a preposition, especially in more formal writing. Ending a sentence with a preposition has become more accepted in some formal writing situations, but you will need to refer to your analysis of your audience’s expectations.For example
This is the computer that the virus was discovered in. (Informal)You can change it to
This is the computer in which the virus was discovered. (Formal)
Trên đây là cách sử dụng "In which". Bạn đọc rồi cố dịch nha 
