40. The half-life for electron capture for 40K is 1.30×109 years. What percent of the original 40K remains after 3.90×109 years?
(A) 33.3%
(B) 12.5%
(C) 50.0%
(D) 25.0%

答案：登入後查看
統計： 尚無統計資料