A:stopped; were still looking
B:will stop ;are still looking
C:have stopped ; were still looking
D:stop ; will have looked
地球不同于太阳系中的其它天体,它的特殊性在于它( )
核电站的核心设备是核反应堆,它是通过____(填“核聚变”或“核裂变”)释放能量的,核能属于____(填“可再生”或“不可再生”)能源,1 kg铀释放的能量约是 6.8×1013J,相当于完全燃烧____kg煤释放的能量.(煤的热值3.4×107J/kg)