（2016高考训练）阅读下列材料，从每题所给的选项中选出最佳选项。
体裁：科普文 话题：科学世界 词数：360 时间：7′
Sir John，a British scientist who won last year's Nobel Prize for medicine，said he had predicted at the time of his frog experiments that the successful cloning of a mammal would happen within 50 years，and that “maybe the same answer is appropriate” for the step to human cloning.Parents who lose children in accidents may be able to clone “copies” to replace them then.
