Answer:
A. This letter is to let you know that...
B. I'm happy to meet you.
C. Thanks for your help
D. Milk is important to us
A. I'll see you next week.
B. Get back to me as soon as possible
C. Did you leave your soup uneaten?
D. Let me know when you're ready.
Explanation:
Informal language is used when communicating with close acquaintances, friends or family. The tone is friendly and makes use of colloquials.
Formal language is used for professional purposes and does not use the friendly, off hand tone of informal language. They are used in school projects, business meetings, etc.