<span>B. Non-Kiowas are presumed to be enemies. is the answer
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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! :)
Answer:
What kind of essay , i'll try to help! (:
C) Celebrate. This would make better sense, since it isn't having a claim to recognize something when it already is a holiday. Observing something would simply be to inspect. Mark is definitely not your answer and you should know that the last ones available aren't reasonable! So the answer is C)