I believe that it is D. I apologize if I'm incorrect.
The discovery that the narrator makes by dissecting his brain is learning that his thoughts require a constant flow of pressurized air because brain activity slows due to low air pressure.
1.opinion
2.fact
3.opinion
4.fact
5.fact
You can usually tell if something is an opinion if it has adjectives associated with it, expression how somebody feels about something, like “best, worst, most____, least____.” Something is a fact if it can be proven. For example, because number 4. says “from the fossils record,” if can be proven that the dinosaurs legs are the strongest by checking the record, making it a fact and not an opinion. Hope this helps
