GRE 里一道逻辑题,请赐教!

GRE 里一道逻辑题,请赐教!
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.

答案是D,我真心没明白...