Translation:A fast rabbit or a slow rabbit?
Right, it's not a complete sentence (neither is the English sentence), but in context it can very well be enough.
Someone might be telling you "I was chasing this rabbit for an hour, but finally I caught it" and you ask "a fast or a slow rabbit?". You leave out [the rabbit you caught, was it] because the context makes clear what you are asking about.
On the other hand: if someone is telling you "My children really want a new pet, I am thinking about getting a rabbit". You can ask the same question, but in this case you leave out [Do you and your kids prefer to get].
Without context or in more formal situations you should always make complete sentences, including a verb. (Like 'speaking with two words' is more polite, but leaving out politeness is easier: "yes" versus "yes please", "yes sir")