there's 4 possible new drugs to cure HIV. A killed the rats, mice and dogs. Drug B killed the dogs and rats. Drug C killed the mice and rats. Drug D had no ill effect. Which should we give to some healthy young human volunteers as the first dose to humans? two answers: d or none because even drug D could cause damage to humans. That is true, which is why Drug D would be given as a single, very small dose to human volunteers under tightly controlled and regulated conditions