题干
-- Can you tell me __________________?
--Sure. For two years.
--Sure. For two years.
A：when you bought this MP5
B：how long you have had this MP5
C：how soon you will buy a new MP5
D：where you bought this MP5
答案(点此获取答案解析）
B
U经过一系列α衰变和β衰变，最后变成
Pb，衰变方程可写为：