Which of the following best completes the passage below "Government" does not exist as an independent entity defining policy. Instead there exists a group of democratically elected pragmatists sensitive to the electorate, who establish policies that will result in their own reelection. Therefore, if public policy is hostile to, say, environmental concerns, it is not because of governmental perversity but because elected officials believe that
A．environmentalists would be extremely difficult to satisfy with any policy, however environmentally round.
B．environmental concerns are being accommodated as well as public funds permit.
C．the public is overly anxious about environmental deterioration.
D．the majority of voters vote for certain politicians because of those politicians’ idiosyncratic positions on policy issues.
E．(E) the majority of voters do not ply wish for a different policy.
，每百吨
核聚变所释放出的能量相当于目前人类一年消耗的能量。在地球上，氦元素主要以
的形式存在。下列有关
和
说法不正确的是 [ ]
在一定条件下若转变为
，不属于传统意义上的化学变化 
和
的原子结构示意图均可表示为
和
分别形成单质的物理和化学性质完全一样 
和
互为同位素 