I believe its D. Conclusion as the narrator finally comes to a conclusion of what they have realised.
Because they are just being silly that is not the reason for most boats sinkings
If I were to read " Stop the Spread of Superbugs" I would ask " I would ask what are Superbugs and how did they start spreading in the first place?"
On the second one I would ask, "How would resisting antibiotics be a threat in 2013?", and " Was here a virus that started?"
