What does a file extension tell you?
A. what the file is about
B. where the file is located
C. what type of file it is
D. who created the file
A file extension is a suffix that is attached to the end of a filename. It typically consists of a period (.) followed by a few characters, such as .txt or .jpg. The file extension is used to indicate the type or format of the file. It can give you information about the kind of content the file contains and what software or application may be needed to open or work with the file.
So, the correct answer is:
C. what type of file it is
https://www.webopedia.com/quick_ref/fileextensionsfull.asp
Read carefully.