下列说法中正确的有[ ]

A．氡核其半衰期为3.8天．1g氡经过7.6天衰变剩下氡的质量为0.25g

B．核反应方程属于裂变

C．根据爱因斯坦质能方程，物体具有的能量和它的质量之间存在着正比关系

D．β衰变中产生的β射线实际上是原子的核外电子挣脱原子核的束缚而形成的

On a vessel making a voyage more than 48 hours long，regulations require that（）.

A.a lifeboat drill be held within 12 hours prior to departure

B.fire pumps be tested by starting within 12 hours prior to departure

C.the emergency generator and lighting system be tested by starting and operating within 12 hours prior to departure

D.the entire steering gear be tested within 12 hours prior to departure