Answer:
1)The great depths of the ocean are totally unknown to us ... What transpires in those remote abysses? ... We can scarcely even guess.
Dr. Aronnax, Part 1, Chapter 2
The narrator, Dr. Aronnax, is expressing the feeling of mystery the seas evoke in humankind and setting the backdrop of mystery that will pervade the book.
2)
It's one thing for ordinary folk to choose to believe in incredible comets crossing space or prehistoric monsters living inside the earth; but neither the astronomer nor the geologist accept such fantasies. The same goes for the whaler.
Ned Land, Part 1, Chapter 4
Ned Land is explaining to Dr. Aronnax why he's skeptical about the existence of any sort of undiscovered sea monster. Anyone who is a professional should know better than to indulge in outlandish theories that appeal to the masses.
3)
I shall pursue that animal until my frigate blows up!
Captain Farragut, Part 1, Chapter 6
With this exclamation the captain of the Abraham Lincoln reveals just how determined he is to hunt the mysterious sea creature.
they ate whole pie!