单选题 It is implied in the passage that the primary difficulty in seeking a safe way to dispose of nuclear wastes is caused by______.

A、 the nuclear process involving the danger of radioactivity at its every stage
B、 fuel for nuclear reactors producing dangerous wastes
C、 the weakness scientists have found in every previous methods
D、 the nature of nuclear wastes together with their lengthy life span

【正确答案】 D

【答案解析】根据文章第一段第一和第二句“One of the major problems of nuclear energy is the inability of scientists to discover a safe way to dispose of the radioactive wastes which occur throughout the nuclear process．Many of these wastes remain dangerously active for tens of thousands of years，while others have a life span closer to a quarter of a million years．”就可推理出[C]为正确答案。