The reader knows the ship will sink so they are now anticipating it all the while watching as the two main characters fall in love and dreading when one will die, this creates tension.
B because the reader already knows what is about to happen to the characters while the others run in chronological order This builds tension rather than shock as it would if it were in chronological order
One reason that The Great Gatsby has now become a byword for the East Coast of the Roaring 20s - the decadently extravagant post-WWI era - is that Fitzgerald was amazing at creating memorable settings. Whether it's the sprawling luxury of Gatsby's mansion.
