The quantity and type of pollution that entered the river last Thursday night suggest that the local auto repair shop is responsible. But the penalty for this type of pollution is so severe that, unless stronger evidence is discovered or the perpetrator admits responsibility, we cannot be sufficiently certain of the identity of the polluter to justify imposing the penalty. Which one of the following principles, if valid, most helps to justify the reasoning in the argument? ['The more severe the penalty for an infraction is, the more certain one must be of the guilt of a party before being justified in imposing the penalty on that party.', 'The more severe the penalty for an offense is, the less likely it is that someone will come forward and admit responsibility for the offense.', 'The severity of the penalty imposed for an infraction should be proportional to the harm caused by that infraction.', "Penalties for crimes should be severe enough to deter people from committing them, but not so severe as to undermine one's willingness to impose them."]