Direction: Which of the following is/are the correct statement/s regarding letter writing?

(I) Informal letters are letter we usually write to our teachers or bosses.

(II) Complaint letters are written to the concerned authorities when you are not satisfied with some service, or you have a problem that needs to be addressed.

(III) A circular is a letter that is sent to very limited people.

(IV) Complimentary letters are usually written by customers who would like to thank a service or product providers for the high quality of their goods or actions.