The correct answer is spaceships.
Science fiction deals with stories that are still years, if not centuries ahead of us. They contain elements that we do not have at this particular moment, or that are not as developed as they are in the stories. For example, robots such as those in the Star Wars franchise, space battles, colonies on other planets, the exploration of space, etc.
Having that in mind, the mode of transportation that would likely appear in a science fiction story are definitely spaceships. We already have helicopters, boats, horse carts, and cars, so there's nothing fictional about those.
