Answer:
The answer to the question: Which rule of evidence would an attorney break if he or she were to ask a witness to predict what would have happened had the defendant behaved differently, would be, B: Speculation.
Step-by-step explanation:
The reason for this being the correct answer comes from knowing that speculation is precisely that, to ask a person to predict, according to his/her own perceptions, what something, or someone, would have done, or how things would have turned out, if circumstances had been what they were. In law, this is a really big break in the rules, because it may lead a jury to a wrong decision on something other than the facts and provable data, instead of just the opinion of someone.