What level of formality do you think would be appropriate for ea

What level of formality do you think would be appropriate for each of the following writing situations?
1. A letter to a visiting professor from Canada asking for permission to sit in on a course he or she is teaching
2. A letter to a close friend of yours, an English major at a university abroad
3. A book report on an American novel you have read
4. A letter to the graduate school of a university asking for information
5. An article for an English newspaper published by your university
【正确答案】：1.medium-level
2.informal
3.medium-level
4.either formal or medium-level
5.either medium-level or informal depending on the topic