The answer to your question is
A
1. Use proper grammar, punctuation and avoid slang
2. When greeting, don't say "hey" or "what's up". Instead, go with "good -insert time of day-"
3. When writing text messages make sure they stay a good and appropriate length.
4. For gods sake please please never say lol or anything of the sort
please
D connecting compete thought
Books that are surrounded by oxygen will turn yellow, so basically, all books since oxygen is constantly surrounding us. Oxygen-rich conditions are very bad for paper, which gives them the yellow tiny. This is actually called lignin oxidation! Lignin oxidation gives it a yellow or brown colour as you said. Yellow comes first, then brown after.
I hope this helped a bit! :)