求解释一道逻辑单体

Editorial：Critics of nuclear power complain about the allegedly serious harm that might result from continued operation of existing nuclear power plants. But such concerns do not justify closing these plants；after all， their operation has caused no more harm than that caused by pollution generated by coal-and oil-burning power plants， the most important other sources of energy.    Which of the following is an assumption on which the argument depends？
   （A） Existing nuclear power plants should be closed only if it can be conclusively demonstrated that their continued operation is likely to cause harm more serious than the harm their operation has already caused.
   （B） Closing existing nuclear power plants would require greatly increased reliance on coal-and oil-burning power plants.
   （C） The harm that has resulted from operation of existing coal-and oil-burning power plants has been significant.
   （D） The harm that a nuclear power plant is likely to cause as it continues to operate can be reliably predicted from the past history of nuclear power plants.
   （E） The only harm that has resulted from operation of existing coal-and oil-burning power plants has resulted from the pollution generated by these plants.
当时做这道题我很纠结，我觉得B和D都可以选。我选了B，我的想法是，题目中说核能的利用产生的危害并不比普通燃料危害大，说明还是有危害的，如果取消核能之后，同时不需要其他危害更大的替代物，那么就Justify了；只有取消核能之后要被普通燃料代替，才不该取消。因为只要是有危害的东西，如果可以摆脱它，就应该取消。当然E符合常识，但是gre考试时是不能有常识的，所以困惑了。答案是E

这道题我也迷惑过，B选项不可取的理由在于它不是直接的假设前提，而是结果性的推导假设，意思是说，我们找的假设应该是导致结果的原因，而不应该是结果产生的后果