题干
Sandy didn’t tell her parents that she was going home because she wanted to give them a _______.
A：gift
B：call
C：surprise
D：note
答案(点此获取答案解析）
C
Rn放出α粒子后变成钋核
Po，α粒子动能为Eα.若衰变放出的能量全部变为反冲核和α粒子的动能，真空中的光速为c，则该反应中的质量亏损为( )